The higher the charge rate, the steaper the discharge curve. That is, more punch in the beginning and less at the end.
This is very pronounced with 1700 NiCd. Charged at 6,5 amps, they got plenty of punch the first minute. After 4 -5 minutes, they flatten out. With cells like Sanyo 3000 HV, the result is the same, but they got so much capasity, that you dont get to the flat-out within 5-minutes in stock class.
The new Robitronic Expert charger, offers a 3 stage charge process: Very high amps in the beginning, medium in the middle and lower amp near the cut-off. Accordingly to Robitronic, this will both give higher voltage AND more runtime. I havent seen it action though, but it seems promising.
Robitronic Expert