It really depends on the bulb. The Phillips 7387 and 7388 will quite nicely. The magcharger bulb usually will blow. The 5c/d bulb does nicely and draws 1A. Something like the hikari 5607 actually needs 3 cells even though it's 6v. Check out the destructive bulb test done by lux luthor to find an appropriate bulb. I'd suggest the Phillips bulbs myself. One is 10w the other is 20w. If you need a potted bulb either the mag 5c/d or rop low or one of tad customs mag bulbs
It depends on bulb rated life, total resistance of switch / electrical resistance, battery state of charge and ...
If rated voltage of above bulb is greater than 100 hours, your set up will most likely work.
Keep in mind that fully recharged hot six serial Eneloops will have over 8 volts.