Heh heh...going to be a few days of reading. But it'll be a fun journey.
Short answer, the Sky Rays are a bit brighter but with the 818 models you might get some which don't pull > 2 amps.
Trustfire 3T6 might be a better option as i have the impression that you have a very very high chance in getting a working light, still plenty bright not to mention efficient. Seriously you are not going to be able to tell much of a diff between the both. You need a TK70/Jetbeam RRT-3 XM-L or DRY triple to do that.....
Our eyesight/vision are processing light intensity as logarithmic in nature, many factors affect the perception, and besides your eyes' pupils just shut down the extra light.
I haven't heard of one Trustfire 3T6 failure. On the other hand, I've heard of many Skyray 3800 failures. Based on that, I'd definitely get the Trustfire.
Go with the 3-cell TR-3T6 without a doubt. Technically the 3800 is a hair brighter but you'd never see with the naked eye. The TR-3T6 is incredibly well built, has better heat sinking, is regulated, works in either 2 or 3 cell arrangement and even on a SINGLE 18650 cell (with a 25mm spacer), and so far doesn't have one reliability blemish on it's record.
I just got mine today and I am stoked for the evening to arrive so I can play with this badboy!
The 3 mode SkyRay 818 that Manafont currently is selling arrived the other day at my door as a 5 mode instead of 3 so if you don't want disco modes, might want to avoid this one until they get that figured out and fixed.
I had the SR 3800 rev0 and now have the SR 818 and TF 3xT6 2 cell version. They all draw about the same current from full batteries (2,85-2,90A) nad comparing tF and 818 I can't decide which one is brighter (also TF is green-ish while 818 is pale-ish). I had a lot of problems with 3800 rev0. I had to replace lens with a thicker one to make it water proof and I insulated the bottom of reflector to prevent short circuit (happened twice). The 818 was also not waterproof until I replaced tail and bezel seals. The TF however is good out of the bubble wrap. The only improvement I see is greasing dropin threads with ceramic paste. If you want ot make it bombproof then replace original lens and lens holder with a really thick lens (custom made I guess). One more thing. When TF dropin is screwed all the way in the reflector outer ring presses against the host. This means that screwing the bezel tight doesn't apply additional pressure to the leds (via reflector). Also while TF has better heat dissipation rev0 and 818 have better heat transfer (leds placed directly on host) and both get hot pretty fast.
To sum it up: get the 2* cell TF version.
*The last time I ws reading about the 3 cell version it was drawing "only" 2.5 amps from 2 cells
According to Manafont's website the 3 and 2 cell versions have different voltage ranges. 8.4 to 12.6 volts for the 3 cell, and 7.2 to 8.4 for the 2 cell. Plus there's a 1/2 amp difference between the 2. Different drivers?