That makes a difference. What CL mode?
Ok I can give you my results. i5-2500k clocked down to 2,0 Ghz, DDR3-1333-CL9 used (Sandy Bridge standard).
CPUMark 99
Sandy Bridge 2,0 Ghz= 306
Ivy Bridge 2,0 Ghz= 316 +3,3%
Cinebench 11.5
Sandy Bridge 2,0 Ghz= 3,18
Ivy Bridge 2,0 Ghz= 3,35 +5,3%
Fritzchess
Sandy Bridge 2,0 Ghz= 6034
Ivy Bridge 2,0 Ghz= 6182 +2,4%
Wprime 1.55
Sandy Bridge 2,0 Ghz= 16,09
Ivy Bridge 2,0 Ghz= 17,019 -5,8%
The WPrime result looks weird, Ivy bridge shouldn't be slower. Maybe a result of your old Bios or whatsoever. You might recheck your 2,0 Ghz results with the newest available Bios (F11a) for your Board.