Your brightest would be the Carley 3.7V 1.7A Krypton Star with NiMh's, but I don't know what the life would be. With NiCads I'd use the Carley 5.0 V 1.7 A KSR. It would be safest to use the 5.0 V 1.7 A with NiMh's also.
With C Alkalines I'd start off with a RS HPR 5.2 V. .85 A bulb (or an Ikelite 5.0 V 1.25 A HPR which is 50% brighter but will really eat up your batteries) and switch to a 4.8V .85 A HPR or 4.8 V .70 Amp to .85 amp XPR after the batteries were about 1/3 used. When the batteries were 2/3 used I'd put in a KPR 3.7 V .75 A bulb to finish them off.
