i've had 2 races on the xm tubulars and am coming from clinchers, typically the raze and the racing ralph.
therefore ... i think the fact they are tubulars and not clinchers is going to weigh heavily on my impression.
i love them.
i am still getting the pressure sorted but they are far, far superior to running the clinchers.
in the mud i found that the centre line stayed clear and i was getting great traction on uphill, off camber slippery turns.
but, i also found that the side knobs packed up and fast cornering was sketch ... but it was looking that way for everyone so, they didn`t make up for my lack of skill in that instance.
i ran them in the dry (95% mud free) last weekend and they were superb. ran a lower pressure than previous and it felt like i was cornering on rails. hooked up fantastically in the grass, hard downhill 180's and loamy muck. saved my lower back a lot of pain and were generally fantastic.
of note was that we had some old xg's kicking it in the basement and the casing on the new vittorias are noticeably more supple than the older, lower thread count, casing.
but, as i have noted. i have not run dugast, challenge, schwalbe etc... in tubular form. first tubulars. but im loving them.
we have a pair in test (290 tpi). been good, esp in the rear, but the knobs are very thin so they wear quite fast when it's not soft and muddy (like norcal most of the time before our 4 inches or rain). i like the vittoria sidewalls - not so fragile, and the 320 tpi tire we have (XG) is very supple.
they've been having some supply problems on the 320 tpi - may not make it this season.
rhinos seem to last longer tread-wise, but don't know too many that have worn out the tread on a rhino before needing to replace it for some other reason.
America's top pro cyclocross racer (hint the only guy to ever podium at elite worlds) had a set on the muddy day at Gloucester. He is sponsored by a different tire maker, so I am not mentioning his name (though he is also from NH, enough hints?). Though he is generally not picky about equipment, he does like good tires, and says he likes these for mud conditions. He was also running Rhinos in the mud.