BTW, a 6 V made a world of difference in my Himoto. The turning is much more responsive and the acceleration is crazy... especially off the start.
Next time you pick up some spare parts, pick up a 6 V too. You won't be disappointed.
How does a new battery pack help your acceleration?? Your Himoto is nitro, right? The only way more voltage would aid in acceleration would be in an electric vehicle. The turning on the other hand would definitely improve with more voltage. More muscle for the servo...
Just for the record, 4 AA ALKALINE batteries equal 6V, just as does a 6V rechargeable NiMH pack.
The ONLY difference is the money you save by not having to buy batteries for the receiver all the time. It's the standard AA NiMH batteries that only produce 1.2V each, rather than 1.5V from alkalines. That's why the NiMH packs have 5 cells. 5 cells X 1.2 volts = 6V...
I myself am a firm believer in NiMH. I have over a dozen of them powering various electronics around the house. I am finally upgrading my Volcano with an OFNA 1600mAh 6V NiMH pack in November when I order my Mini Quake and other miscellaneous goodies. TGFQB (Thank God For Quarterly Bonuses!!!

Check it out down below...
PS - Standard 1.2V AA NiMH batteries for the transmitter are just fine. It doesn't require much juice at all. I picked up 8 Duracell 2650s at Wal Mart a couple weeks ago. I believe they're the largest capacity on the market today, which in turn offers the longest useage/slowest drain. It's those darned servos that drain the batteries, mainly the steering.