I wouldn't expect "out-of-sight" performance out of that combo. I have a .91 4-stroke in my .40size GP Extra, and it's decent performance, however, I've seen and had better. The plane is built very decently too(I have to say...I built it..hehe). It does have totally unlimited vertical, but with some of the power-to-weight ratios as high as they are..I've got planes with higher ratios that climb out alot quicker then that one.
The .40size Extra is NOT alot smaller then it's slightly bigger brother the .60size. I've seen the 2 planes side to side..and not a big difference. Matter of fact, the first .60size I saw.. was on another pits table at my flying field..and I had to get the 2 planes(mine and the other) nearly side to side to tell a big diff, and then it wasn't as big as one would think.
Go with a 1.20 at least.. It will handle it well. It's not a 3D ship by any standards, unless extreme measures are taken, so for IMAC style of flying, a 1.20 will pull it through anything gracefully I'm sure. Just as the .91 does for my .40size, which it really does do a nice job for that style of flying.. I just know I would put at least a 1.20 in the .60Extra. Good luck.

PS....I don't think you'll need a fuel pump of any sort. The 4-strokes do have a good draw on the fuel.