Looking in the Nikon SB-910 manual, it shows that both 2,600 mAh and "eneloop" Ni-MH rechargeable AA batteries give you an approx. minimum recycling time of 2.3 seconds with this flash. However, I find this unusual since Sanyo Eneloops are typically only 2,000-2,100 mAh. Does anybody have experience with Eneloops in this flash? Are they just as good as higher (ex. 2,600) mAh rechargeables? I already own a bunch of Eneloops and don't want to have to buy other rechargeables if I don't have to.
Eneloops are "better" than the regular type. Because...
The NiMH rated around 2600 mah are "regular" old NiMH, which means they lose charge just sitting on the shelf. In a month or two, they will be near dead (needing recharge) regardless if they are used or not. But if you recharge the day before your use, this is of no consequence. But if you get them out for shots next Christmas, you will discover a big surprise.
The Eneloop type (called low self discharge) hold the major portion of their charge for a few years. There are several of these brands now, all licensed from Eneloop, which developed it. These are marked "low self discharge", or more often, "precharged, ready to go", meaning they did not self discharge sitting in the store. They should mention long storage life. The factory does not fully charge them though, it's still a good plan to recharge them first.
So... if the larger 2600 mah capacity will be of use for your big shoot tomorrow, you may want the regulars. Or you could always just carry a spare set of Eneloops, and have 200% capacity. If you only shoot a few flash pictures a week, you will really enjoy the Eneloops always being capable to go.