the drivers are 7135 based, when you see 7135*4, it has 4 350 mA chips on it, if it says 7135*8, it has 8x350mA chips which makes a 2800mA/2.8A driver which is twice the potential of a 7135*4 driver. I've recently(the last couple days) been messing with 7135 chip stacking, and I don't believe the chip count to light output is linear. Say for example, 7135*4=500 lumens... A 7135*8 =/= 1000 lumens and a 7135*12 =/= 1500 lumens. It's more like 7135*4=500, 7135*8=750~800 7135*12=1000ish?! all numbers are just examples, just trying to explain my point. The 7135 chips allow current to flow through them, so they really just open up the potential for more light. im still just getting my ears wet so don't assume I actually know anything, just sharing my experiences.
honestly if I was going to buy another S light I'd go for an xml2-t6-3c with a 7135*8 driver. The color rendering is much nicer and real(compared to actual daylight color rendering on the eyes) and the lumen loss from t6-U2/u3 is negligible, if anything the t6 may or may bot even be close to the same lumens due to lower forward voltage. I don't quite understand vF yet.
Link to Simons ShenzenElectronics store.
http://www.aliexpress.com/store/330416
if you want to get one a little faster check out the s6 from mtnelectronics but I think they only had 7135*6 :( I would have bought a couple more s5/s6 from him if he offered 7135*8...probably go for an s5 host anyway soon.
oh, a 7135*8 is going to take a solid 5-10 minutes on high mode to get hot... i don't know who would need that much light for that amount of time. They have potential to get really hot after 15 minutes but realistically your going to be using low or medium 9/10 times and high only in Short bursts. I put 13 350mA chips and 3 380mA chips on a circuit board, then stuck that in a s6, and it did manage to get pretty dang hot pretty dang fast, probably less than 3 minutes and it was scalding hot, but the light output wasn't increased nearly enough to be worth it with an xml2-u3-1a on aluminum. i think 12 is a good number lol.. The only time I had my s4 scalding hot was when I had it tail standing on high, thought it was low mode, for about 20 minutes, maybe longer. That's the only time its been too hot to handle.
these are floody lights, no ifs ands or butts about it, a smooth reflector will pick up a couple hundred foot of light though, available through the aliexpress store. They say only certain models but they fit the s4, and I'll bet they fit most of the others as well.