I think the 808 is played out. The money they’re fetching is way too much for such a limited and overused piece of kit. I think you’ll regret not getting the Tempest. Tempest + Octatrack is such an amazing combination.
The Octatrack adds the ability to real-time sample, slice, mangle, manipulate your Tempest beats. Plus it adds the effects the Tempest lacks.
For your standard fare drum machine sounds, to me you can’t justify spending 10x what an AIRA TR-8 costs for something that sounds maybe 10-20% better.
You could get a TR-8, or a Tanzbar, or an Acidlab Miami and still get the Tempest / OT combo. That will offer so much more variety and satisfaction than blowing your wad on a “real deal” 808.