I've been thinking about batteries lately.  My initial thought has been to simply run my full sized 2s lipo packs.  I've never run a lipo back to back with a nihm pack to see what the difference in speed is, but I've read that difference is noticeable.  I've been thinking about running some 7 cell nihm packs instead.  The nimh packs will fit in with my brushed electronics and will mean I don't need to buy a lipo cutoff alarm.  Also, in the mid 80's running 7 cell packs was very popular and with my more modern Trinity P2K Pro stock motor, the car will be as fast as a modified car from that era.  The only real drawback is the added weight, but this is more about fun than building a serious race car.  I also don't have to worry about maintaining the packs like I do with my race lipos.

Cheap Battery Packs.com will custom build packs.  $26.25 for a pack built to my specs is a pretty good deal in my book.