I would suggest increasing the voltage to like 1.5v if you want to top 2.6. That's what i had with my 3200. The fact that others get good overclocks out of stock voltage does not imply that you will be able to do the same, it all depends on luck. Don't worry about higher voltages, just keep a close look at the temps.
DFI LANPARTY UT nF4 Ultra-D Socket 939
AMD Opteron 165 Dual Core 334x9=3GHz@1.52v
OCZ Platinum Rev.2 2x512MB DDR 400, firstname.lastname@example.org
160 GB Seagate Barracuda 7200.9
Antec TRUEPOWER TRIO 550W Power Supply