the mini-V ESC/reciever is a good match and can handle more upgrades.
[link]http://www.horizonhobby.com/Products/Default.aspx?ProdID=LOSB1087[/link]

45 bucks though...ouch. I found a cheap traxxas esc and an old hitec reciever and use those in one of my RR2's.
The most difficult obstacle to overcome when upgrading the ReefRacer2 is the center of gravity IMO.

The motor placement makes the nose want to plant itself and submarine at high speeds (higher than stock). I suggest you keep the weight as far back as possible when placing larger packs. I have cut mine up significantly to try to set the boat up better, but with limited success.

In my experience 8 cells stresses the ESC too much, so test a bit, then check temps.
I also tape my RR2's up...even though it doesn't seem like they need it, I've learned my lesson too many times...take the time to tape the hatch as well as securing the decklids.
check this to read about my lesson...
[link]http://www.rcuniverse.com/forum/m_5998549/anchors_5998549/mpage_1/key_/anchor/tm.htm#5998549[/link]