I have a 4*60 with a YS .91FZ (supercharged 4-strk) which allows unlimited vertical status easily. Will hover and will pull out nicely. I have a APC 15x6 that works well and also use a APC 14x6 (15x6 trimmed down). I think the .91 2-stroke will give you very good performance and possibly may allow you to go veritcally unlimited. I'm pretty sure it will though. If it is a kit, try to keep it light and I think it may go unlimited. The .91 2-strk, has tons of power if you can rev it up high, but this is going to fly you faster. 2-strks make their power up top and 4-strks make their power lower. The .91 2-strk may not torque roll well, but it will hover it. Try a APC 13x8 or 13x6 for the 2-strk .91 to start off with.

The 2-strk .91 will make more HP than a .91 4-strk, but the 4-strk has way more torque. HP in real life means nothing unless you are going for speed. HP determines how fast you go and torque determines how fast your get there. If you can find the happy medium to allow high revs, but low speed then that is the prop that you want. Large in diameter and low in pitch is the way to go for pulling power. For speed it is the opposite, low diameter and high in pitch.

DTB