Just to share a few things you might want to do with the Avistar.

One, the extra weight shouldn't be a problem as it looks like you only added maybe 7 to 9 oz with the bigger engine and balance weights.

Two, if your radio supports it (don't know if you have the stock Avistar radio or not) install two aileron servos and set up for flaperons. I have this done on mine and it makes a big difference on landing speed. It really just floats along. This can be done very simply by using slightly smaller servos. I used HS-81s and they fit side by side in the stock servo mount at the wing join. No adjustments to the control linkage required or anything, pretty much plug and go.

I picked up mine from a guy who had crashed it and broken of the firewall. After fixing that, I find that even though its a 'trainer' this is one of my favorite planes.

Duke