I agree with linc; anything higher than 2s lipo or 7 cells, use an external switching BEC.
Yes, I have two 125's. One is in my Ofna Ultra GTP (road car) on 5s and Neu 1512 2.5d. The other is in my Hyper8 buggy on 4s and Neu 1512/2d. In both cases, I made a mounting plate that doubles as a heatsink. Works great, especially if you use a little thermal compound. These ESCs do tend to run warm otherwise.