I say quit molling over your choice. The bells been rung. Put the 61 fx on it. Fly it. If you like it - GREAT! If you don't, then sell the 61 fx and buy something bigger. Sure you might have to do a little more work on the plane to rebalance it after putting another engine on it, but working on the plane is half the fun isn't it?

To modify a phrase I learned from amateur telescope making: Fly more - Worry less!

Enjoy.
Brad