Volca, obviously 
Well, you have the issues clearly laid out, and it sort of seems like you have come up with the msot reasons for wanting the AR. As you already have an OT and know that you love the elektron workflow, I’d say that’s the #1 factor after the basic sound.
Some + and - on the Tempest, which I own. You don’t have a noise source in the traditional sense, you have to use noise waveforms on one of the sample oscs. In practice this is not an issue. The presets suck horribly, I deleted them all but I have been very impressed with the sounds I can get out of it. the modulation matrix on the Tempest is a big plus, you can make enormously expessive instruments, albeit at the expense of programming time. And of course the engine is super-flexible so it’s actually a great synth, indeed many of us feel it’s somewhat better as a synth than as a drum machine. Put it this way - I want an AR, but I’m having a hard time deciding whether to sell my Tempest or keep it and sell the A4, which I love but have never totally bonded with, or lose both and pick up a prophet 08 (but I’d miss the big pads and the high pass filter). Space is a factor as well as money.
Some negative Tempest issues: #1 for me by a mile is that the LFOs don’t run free. The manual says they do but what they mean is ‘not synced to MIDI clock’ (they are synced by default). So the LFO retriggers every note, which means you can’t have LFO-sweeps over notes or drum hits unless you do something like sending CV from an A4 to the pedal input or apply an external effect. This is fucking stupid and I blame the prog-rock roots of DSI, because why would you make a sequence-based dance machine that didn’t let you do things like LFO filter sweeps.
Synth can’t currently play legato, if that matters to you. MIDI implementation is primitive by modern standards, and not documented at all (although it’s broadly similar to the Mopho).
Development work on new versions of the OS continue in theory but in practice have slowed to a crawl, and the developer has a habit of promising to fix stuff, making several progress reports, and then saying that it can’t happen for a long time or maybe never, and anyway it’s technically complete so leave him alone already, and/or blaming the hardware limitations because there isn’t enough memory on it. I would be extremely reluctant to ever buy another DSI product because of this. Elektron also have unfinished operating system business, but at least they don’t make promises and issue detailed progress reports only to suddenly change their minds. If you buy a Tempest buy it as is, not for its future potential because otherwise you are going to end up very very frustrated, like a lot of other people. The machine is great but it’s like the parents don’t care and it dropped out of high school before reaching its full potential.
The sequencer…it’s different from Elektron machines. A little more simple and accessible, great display and intuitive to program plus the pads are really lovely to play on. But it’s also very linear and not really interactive like the Elektron ones. I rarely use it, although it’s nice that it does 8 bars and up to 32nd notes. It’s fine if you know what you want and want to lay out song sections in a conventional fashion, but I’m addicted to he variable track/pattern lengths on the Elektron sequencer, being able to slide patterns back and forth in time, microtiming, p-locks.
Onboard effects on the Tempest are pretty simple, 1 knob each for distortion and compression. Nice in theory but in practice I almost never use them, too crude to really shape your sound and they feel a bit gimmicky because they go across the whole mix The MIDI-note-repeat delay thing works and you could leverage it for weird and interesting effects with careful modulation matrix programming, but it isn’t all that musical to be honest. You need external effects with this machine which may mean additional cost, although since you have an Octatrack you could do quite a bit with the onboard effects on that. I think the effects on the AR are one of the biggest draws, although they apparently don’t work on external sources and you only get delay and reverb, having individual FX levels for each track and fully programmable FX parameters locked into the sequencer is a huge deal. The delay and reverb in the Analog Four are fantastic and the AR seems to have the same system, very musical and flexible.
A few things the Tempest does better as well. Although it’s slower to program, you can get really deep and expressive sounds from it since it’s basically a 4 oscillator synth with two sub-oscillators. The extensive modulation capabilities make it sound very ‘alive’ and distinct. I have no problem getting almost any sound I want from it, although I haven’t quite managed to emulate the famous 909 open high hat sound. You can totally get solid kicks from it despite what some people say, but it takes a little work. The user interface is not perfect but it’s very very good and and it’s very pleasant to use for hours at a time. I think the physical and user interface design is a bit better than Elektron stuff to be honest.
You can dial in a wide variety of user scales when playing synth sounds and this is really wonderful. I wish the OT and other Elektron gear did this instead of just offering major and minor. Great for jamming. The pads and touch strips are likewise great, really inviting and responsive and some of the best controls I’ve used on any gear. The knobs are a little lightweight and plastic by contrast, very much for programming rather than performance. 32 sounds I’m not so sure about…they’re in 2 pages of 16 so realistically you’ll use the top 16 90% of the time, and if I understand the AR manual correctly you can access any of the 128 sounds in the project by p-locking, it’s just not quite as accessible. I rarely use 16 drums in a project but it’s great for setting up drums plus bass sounds plus a bunch of textural stuff.
In sum, a more enjoyable synth than the A4 in many respects, but IMHO an inferior drum machine to the AR.
