I have heard the X-1's (I own them), the UR2's (own them), and the UR5's (Grover sent me, I listened for a little while; but I returned them when he told me there was an even better version out, which is on its way).
While I may not "gush" like Eyeteeth does (sorry if that's offensive), I still concur in general with his findings.
The X-1, in my system, just seems to open things up more top to bottom. The analogy of letting water travel through a larger pipe is a good one. That is literally the sense I got when the X-1's were put in my system.
That said, the X-1's are not for everyone. They seem to be ruthlessly revealing! I consider my system very good (Eastsound CD-E5 feeding Belles 250i integrated, feeding Eminent Technology LFT-16 speakers; or, the E5 feeding a TrevorNetwork-built Max'd Dynahi).
With most other cables, this sounded great. Yet with the X-1's, it opened up even more, seemed that much more transparent. At the same time, the X-1's showed me I had a VERY slight midrange glare or sheen. At first I had thought it was the cables. But in trying about 4 or 5 other cables, I realized it is barely there, and the other cables may just be masking it a bit. I was lucky that toeing the speakers out a bit ameliorated the problem for the most part, without causing other problems. It doesn't bother me at all now.
Because of this revealing quality, other cables may go better in some systems than the X-1. The UR5 I had was VERY smooth, and extended on both sides very well. It was detailed, transparent, and very noticably better than the UR2, the last Grover version I had.
In my system, it was not as open and transparent ultimately as the X-1. Toeing my speakers in again revealed the glare, but it was less apparent. The music was still incredible, though, and I look VERY forward to hearing the U6.
I think the Grover's and the Oritek's are indeed "giant killers." I have heard cables in my system that cost up to almost $1k (Nordost Quatro FIl, Ensemble Dynaflux, Cardas Neutral Ref, PLENTY others). Any cable that competes with these cables, and betters them in many or all ways, is a giant-killer in my book. Is it the end-all? Maybe not. But even giant-killers can be killed themselves
And yet, as good as the UR5 is, the X-1 takes a step even higher in my system! The transparency and openness, and its ability to seemingly just let the music truly flow, is like I have only heard with some BIG dollar systems. I remember this type of feeling of ease of flow and transparency from a system that was priced around $40-45K (FYI, it used Nordost Valhalla cables).
Bottom line: both of these cables say a LOT about the price/performance ratio, and about the capability of cables REGARDLESS of price.