The speed would be about the same but the acceleration may suffer a bit.
I would recommend the 2/3a cells simply because they are smaller and lighter than those cells. Since you are only running five minutes and all. Weight with these small cars is important. If you want, I can build you a four cell pack of 2/3a cells in whatever configuration you like for $15 shipped. If you need a connector, they are extra. We can work something out. Let me know.