I'm thinking of putting an aimpoint in a 20" upper set up for varmit use flat top freefloat tube etc. would it work ok for varmiting at a 200 yards? if it had a optical zoom? witch model would that be with a optical zoom?

Can you see your targets at that range?  From what I hear, 2x Aimpoints are terrible.  Better stick to a Leupold or something with higher magnification.

If you want to use a red dot scope then nothing could be better than an Aimpoint. You state that 200 yrds is your limit. Great, as the Aimpoint will work perfectly at that distance. Use the 50 yrd zero procedure and the bullet will stay within 2" from zero to 200 + yrds. A 4 moa dot will work best. Anything with a zoom feature will require some form of parralax.

This can later harm your point of impact.