FWIW, I use a 1512 2d on 4s and it works fine. Even geared up on 46/16, the motor is perfectly fine and stays cool (even for me). I tried it momentarily on 6s and it still is fine, if too fast to control!
The Neus seem to not mind higher rpms. If you run a high rpm, just gear down a bit to keep things controllable. As long as you stay under 50k you should be perfectly fine IMO.
In my Ultra GTP project, I plan to run a theoretical 62k rpm on a 1515 (but the rpms won't get that high because of wind drag).
I haven't had a chance to run it yet, but I have a 1512/1.5/D/F in my buggy. I just today got my 4s Polyquest 5000mah pack in the mail. I'm still waiting for my charger.
I have an 11t and a 12t pinion to start with. I may need to gear down a bit more but I want to see how it does with the ones I have first.
With the RCM motor mount I'm not sure I can get anything smaller than 11t to work without some "modification".
I'm running a 1512 2.5d/y in my 8ight on 5s. I'm running a 14t pinion, stock spur and a 5s 4000mah MaxAmps pack. I have not taken temps but I can run for a very long time (25 min+) and neither the motor nor the Quark 80b get more than warm. It's way too fast for the track like this but I can rip up a soccer field just great!
For a race buggy I think 4S is definitely the way to go for a 1/8 buggy. I am running a 1512 2.5D in my XB8EC with a 17/48 gearing. I'm running a 4S 5000mAh MaxAmps pack with a MM and my top recorded speed (via Nomadio React speed sensor) is 42 mph.
I tried a 3000 KV range motor on 4S in the buggy before the Neu came in and it was thermal central. I thnk over 3000 kv is just too much for a 7-8lb buggy. Even on 3S you'll just be drawing too many Amps. I run a LMT 1930/6 (~3400 kv) in my CRT.5 (~4-4.5lbs) on 3S and it is an absolute perfect setup.
I have the XB8EC punch control on the MM turned up and the 2.5D will still pick up the front wheels sometmes. When the MMM comes out I plan to try out a 5S pack with 15 or 16 gearing - should be totally insane.
“Everyone has a right to be stupid; some people just abuse the privilege.”
I think it really depends on gearing for motor choice. A 1512 or similar size motor seems to be the best bet for a buggy. Slightly higher kv allows for lower gearing and the higher rpms make up for less torque. This assumes that a high quality motor is employed.
I have a hyper 7 buggy and run a hacker c50 8l on 4s thru a mm. It is geared 12/46 at the moment, and I need to mod the motor mount to fit the optimum 11t pinion. It works very well and does not get hot, even after 25-30 mins. I did not think that it would work very well, but it does. I do not think that a feigao would do it though.