Just picked up a Stingray X clone with the carbon fiber sleeve. The voltage drop is slightly lower (surprisingly) than the SS version, and a bit lighter too.
@Forkeh you could do far worse than to pick one of these up,I guarantee you won't be disappointed. Floating silver coated 510 pin, smooth as you like magnetic switch, extremely low voltage drop, small light and beautiful as hell. Go for the Kepler version, you can get them for around $25 from FT, delivery took about two weeks.
SS version
I have glaced at that particular SKU for the last 6 months or so, going back and fourth over if I should get it... I wanted a kepler one-18650-tube stingray x in SS, but as I couldn't find it, then this was the only option. I wasen't sure if carbon-fiber would diminish the infamous low drop of this mod(kepler 1-tube especially), as i'm not that much in the know about such.
Current travels through least resistance I believe, so the SS would probably not even be used and the SS added wouldn't really do anything except making the mod more durable i'm thinking. I don't know how two metals in parallel relates to current flow though honestly... However, your test of the VD made me finally go buy it, so thanks alot for testing it and posting! Oh, you did relate the test to the SS 1 tube kepler right? Sorry if I misunderstood, but I seemed to remember you had a kepler SS stingray x...
I also ordered a copper kepler pinless-510 topcap(20x0.5) to go with it... I know you've compared both types previously(pinless-510 vs normal topcap), but the included is brass and the normal topcap is copper internally, so maybe it can push alittle more with that than your tested 0.03v diff, if I remember right... I'll test of course

Anyway, this design is great, with wide-friction-point copper to copper connections and wide contacts and battery-rattle/atty auto-adjustment and floating 510 etc... Well, using a rice-pin isn't the greatest imho, but OK... Also, I prefer recessed buttons, but nonetheless...
Also some state that the switches of kepler SRX's isn't as tight as the SXK versions(3-tubes), tolerance-wise, but that could probably be fixed/workarounded by a thicker homemade rice-pin... I saw a youtube vid of this mod and it was very wobbly, but it's just the rice-pin most-probably...