RE: Diamond Dust mods
1. You will be disappointed with the .28 if you want 150 mph. To get 150, it will take a Jett or similar high performance or racing motor. Standard servos are fine with either of your motors. If going for 150, I would use stronger servos.
2. No mods are necessary for the 40.
3. I would tune for an APC 9x7. Readily available, and less expensive than the pylon props. You may break one every now and then landing. Hopefully, you can turn a 9x7 16k to 17k. I would expect 120 +/- mph.
There is a big difference between a 120 mph D-Dust and a 150 mph D-Dust, at least to me. The former is very fast recreational place. The latter is a missile.
Just my thoughts.
Paul