4.8v, NiMh in 12仔 is in the past. Everyone uses LiPo because it is more convenient. Car companies have re-deigned all the cars to fit LiPo; hence no more t-bar cars now.
I believe people use between 4.5T to 5.5T for 4.8v. The speed should be similar to today's 4.0T to 4.5T with 3.7v. Run time is about 8-10mins as well.