I have an X and have lifted most of the following from another thread:
I bought the frame in January 2012 and transferred the majority of parts across from a Kinesis Convert2, which I chopped due to having weedy road rim brakes. My X is a Mk2, meaning it takes 160mm rear discs, but doesn't have top pannier rack mounts.
I guess most people buy frames from the web nowadays, relying on reviews and generally being quite happy with what they get. Personally, I could see myself happy with a CdF, Peregrine or Kaffenback - they're all subtly different takes on the same theme, although at a wide range of prices.
The finish of the frame is great and, despite an iffy road.cc review (balanced by lots of positive ones), I've found it rides perfectly for my needs as a workhorse and tourer with occasional gravel roads thrown in. It's worth noting that I've had trouble fitting a pannier rack due to the positioning of a BB5 calliper - the pannier mounts only work without discs and I can't even make my Tubus QR axle adapter fit to get around this. You shouldn't have this problem with any frame that has the disc mount inboard.
I've searched for references about the X's weight and can only find Cy's forum posts saying it's 4.1 lb for a Medium. The Roadrat is 4.4 lb-ish, so I guess that's credible. Either way, it's definitely among the lighter steelies, probably because it's shorter than the others.
The best and worst thing about the bike is that it has accidentally become my main bike. It's so versatile that I'm doing ten hours on it for every hour I spend on my Cotic Soul. It seems a bit perverse to be spending most of my time on a workhorse when I have nicer kit in the shed.
Despite this, the X just works so well even wearing relatively humble kit. It also looks very good in real life - I get a lot of compliments.
The drivetrain is a 9-speed mix of Tiagra 4500 shifters, 105 5700 34/50T chainset, 105 mechs, XT chain and SLX 11-32 cassette. Wheels are XT M756 hubs and Conti GP 4 Season 28c tyres on Mavic TN719 rims. Brakes are BB5s and finishing is Easton EA50. It weighs under 23 lbs and, although I'm tempted, I think I've reached point of diminishing returns in terms of upgrades.
You'll see that Cotic only have the 58cm frame left and I hear a whisper than the X will be replaced with something else. I was thinking of a Roadrat in replacement, but if Cotic do a "Y" with proper pannier mounts then I will definitely go for that.