Personally, I think the Peak is a better synthesizer than the A4. I think it sounds better and I think you can do more with it. But that’s a personal opinion. The A4 is multitimbral, where the Peak is not - so if you want to make a live composition, you might get more from four separate A4 monophonic voices than one Peak patch despite eight note polyphony (Digitakt can only sequence four notes on one step in any case - though it might work to double up on two midi tracks, it’s probably not that intuitive). You might also find more synergy between the A4’s internal sequencer and the Digitakt - matching up pattern changes, and so on.
But the Peak is very controllable via midi and will respond to p-locked/LFOd parameter changes very nicely. It’ll be great for creating sample material as well. It has a strong feature set - three oscillators, lots of modulation (including oscillator FM), good effects, etc.
To be honest I’d say everything works well with the Heat. But actually the Peak has loads of overdrive options already built in - it has pre-filter drive, post-filter drive and a distortion effect.
This demo gives a good indication of what the Peak can do, and goes to some interesting places: