Nice choice on the Tiger 2/Tiger 60 as a second plane. The only significant challenge that moving up to .60-sized aircraft should present you with is trying to get a larger aircraft packed up into your car.

Larger planes are more stable and easier to see. There is no other difference from an operational standpoint. A lot of pilots stay with .40-sized airframes so they can reuse the engine from their trainer. If you're planning on keeping your Avistar running so you can fly them both, then this is also a non-issue.

Good luck and good shopping.