Dean's Connectors and LiPo's made a huge difference
I have a stock HPI Blitz. I went and bought two used, 4500, 25C, LiPo's and used them for the first time today. Wow, what a huge difference. Just love the amount of current that can be drawn from these guys without sagging the voltage! Where before I couldn't clear certain doubles with the NiMh, I could do so easily with the LiPo; no other changes! I must have had a 20 to 25 minute run on those batteries too.
And, even with my NiMh, the Dean's connectors make a big difference too. Those Tamiya connectors need to go the way of the Dinosaur; there's just way to much resistance in those things.
If you not sure to get LiPo's and Dean's - do it. It's totally worth it!