I find this thread interesting,
http://www.tbreak.com/reviews/article.php?cat=grfx&id=618&pagenumber=2
they tested some graphic cards, including gtx280 single, sli, agains 4850 crossfire, 3750x2 crossfire
Testbed
CPU: Intel Core 2 Extreme QX9770 3.2GHz
Memory: 2 x 1GB OCZ DDR3-1600MHz Memory Modules
Motherboard: ASUS Striker II Extreme
Optical/Hard Drives: Generic 8X DVDRW, Maxtor 80GB 7200RPM/8MB Cache SATA
Monitor: BENQ 24" LCD with 1920x1200 Resolution
Operating System: Windows Vista Ultimate - 32bit
PSU: 1000W Silverstone PSU
The top score of 3DMark06 gots to 3870X2 Crossfire 18,931
Their single GTX280 scores 16,447, while i get 16,675. Now I am happy.
Still, it is less than the 19k score posted by closed_deal with 3870 crossfire