with the .25, after adding the lead to balance it, you would be able to fly, but you would have a very hard time doing a loop. It would only take off from a smoothly paved runway, and then it would take about 200 to 250 ft.

Best advice... NO!

The 4*40 is a GREAT airplane with a mild .40. It will do all the aerobatics it was designed for quite well with a .40 FX (or even a Magnum XL 40) It will HOVER on a .52 4-stroke with power to spare. It will just limp along feebly on a .25