its not, hands down, its almost never beats it. the majority of games are faster on the 4890 at 1680x1050, 1920x1200, and the 275 edges games at 2560x1600, I assume due to simply running out of general raw "rop" power for so many pixels. The fact is 99.9% of people AREN'T running at 2560x1600, so the 4890 is the better choice, not to mention more available and cheaper which kind of makes the 275 rather pointless.
AS for loud, my 4890 is silent, its sure as hell loud on boot when it uses 100% fan speed, infact its insane, in gaming it never gets above 32% for me even clocked at 950/1150 which it did out of the box(where it ends up faster than a 285gtx) for a card I got for £159.99 thats a damn good deal.
the 275 is a VERY good card, its maybe not quite fast enough over a £150 260 to be worth the price but its still very very good.
I would imagine the 275 sli with faster clocks alone would be faster, though the extra pci-e bandwidth would probably also give it an edge over the 295gtx. As in even if you could clock the 295 cores to the same level as 275 cores assuming great cooling, I still think the 275 sli would be faster in certain situations, maybe up to 10% sometimes.
4890's seem to scale great in crossfire which seems to improve often, though baring Crysis I don't think theres many games out there at 1920x1200 or below where sli gives you a significant and noticeable boost in game performance. Theres probably 2-3 games where a single 4890/275 couldn't push 60fps average at least with max settings where for the majority anymore is rather pointless on LCD's.
Honestly if you want a gaming card I don't think theres any cards to be buying other than a 4770, a 4890, or a 260, and any combination of those cards in sli. 275/280/285 simply aren't much faster than a 260 but cost a heck of a lot more, you get into tri sli 260 price range before you get into 285 sli prices, its an utterly pointless card for anyone.
Likewise at the low end the 4770 can't be beat and in crossfire its fantastic also, its only limited by max of dual cards(afaik). The 4890 is the fastest/best/best value card in the range for single cards, overclocks well, widely available, runs quietly (for me, rather crap fan tbh, a £5 zalman fixes the cooling to completely silent in a 5min job that yes, you shouldn't have to, but there you go).
