[jhautz]

I think the answer to how many volts is to much is going to be different for different servos and recievers. I know that the Spektrum Rx will run up to 9.6V I believe and servos are rated for anywhere from 5v to 9v.

I have personally run my nitro buggy on a 2s li-ion pack (8.2v peaked) with no regulator and have had no issues at all. The servo is blazing fast at that voltage, but its still going with no problems. There may other servos and Rx that wont take that voltage. You will have to do some research on your specific equipment.

All that being said... I think you will have a much better chance of everything surviving a BEC failure running on 2s lipo vs 4s though so I dont se how it could be a bad thing with the exception of the pack that caries the BEC load will wear down quicker than the other pack so you will ahve to be carefull not to over discharge that pack.