NiMhs - 7 cell pac, 4400mah charging at 4.4amps would need at the most roughly 10v (remember you have to overcome pacs internal resistance) X 4.4a = 44watts. As long as your 3300s are 6 - 8 cellpacs, you'd be fine with a 50watt charger.

C&B RC - one note - all your calcs use nominal lipo voltage. There will be a few moments where the max voltage of 4.2v/cell will determine watt requirements. When mine switch from CC to CV portion of the charge, there's a few moments before the current stats going down, this will be the max watts needed.

Gets more important as cell count goes up as you pointed out.