This application is not especially high drain for a 26650. At full output it is going to be right around 7 amps. The choice of protected or unprotected is up to you, but in general unprotected cells will provide higher output because there are some losses in the protection circuit. Any 26650 cell from a respectable manufacturer should have no trouble delivering 7 amps, so avoid the ultrafire, trustfire, or any other name ending in fire, you are probably going to be OK. Generally the very high current cells sacrifice some capacity to be able to deliver 20+amps so the 5200 and 5500mah or even higher capacity cells from reputable vendors should be fine. If you want delivery in the immediate future, buy from someone based in the US. I’d recommend Mountain Electronics, they have an excellent reputation and good pricing, www.mtnelectronics.com. They also offer the 23650 cell, which allows you to operate the SC26 in a short form factor, or perhaps higher output using a pair of 23650 cells and the longer form factor.
The preorder page says that there are 26 days from today left in the preorder so that puts it right around the late first or early second week of August.
Just keep in mind what happened last time someone tried to guesstimate shipping dates for this light. At least the BG order page is reliable with regard to back ordered vs shipped status.
I would expect these to actually start arriving sometime around the middle of September. Much patience is required with these sort of things. Fingers crossed that I’m wrong!