Id go with the Kat 70 Ive just got my second Kat40 now (after running the first through its usable life cycle) an absolutely love it. Cant wait for the 70 to arrive, should be here before to many more weeks. Id take another look at the bipe farther down the road. The Kat 70 at $200 will be hard to beat. www.AccelHobby.com
Luck with whatever you purchase.

Oh btw Id pass on the tower 51 an the magnum engine.