Check the site you can put in any gearing you want for most bikes and get all the info. I would check for you but off out!
The 800 does yeah, really strong, the 675 is less strong through the whole range than the newest 675 but has more Rev
If you want more power luke pretty much hit it on the head, When I had my Street triple tuned I had power commander, decat, race stacks, MWR filter, SaI removed and was running an SC project GPM it went from 90 bhp at the rear to 103 and torque from 44 to 50..
I have overbored block and modified gasget with these to go. Bought used engine to build up to SS tune, it waits courier on a pallet at T3. I dont even have this vintage bike yet, but time will come .
You've got the can so I'd finish getting it breathing properly first. Race air filter and trumpets to get more air in and then some decat headers to help get it out. That's the easy bolt on stuff. Then get some race cams in there. After that you are spending a lot of money for small gains. It will need a power commander or similar to map in all the new parts.