I'm not a racer, but I use them in a few of my MTs. To get around the voltage diff, I run one higher cell counts than I'd run using lipo. If I was running 4S lipo, I'd run 5S life (I use the 2300mah a123 cells), that makes up for teh voltage diff - 16.8v vs 18.0v. Its closer at 5S lipo and 6s life - 21.0v vs 21.6v.

Course if you wnat to run 2S lipo, its too much of a jump to 3S life 8.4v vs 10.8v.