Ginga, i have found the reason why you are not seeing an improvement with the systool core voltage increase.
Asrock official bios1.4 has a bug whereby the manual voltage settings of 1.45v are only applied on the first boot after setting them. On subsequent boots the settings revert back to auto and a startup vid of 1.4 is applied.
i hadn't noticed this because cpu-z was showing 1.44v with the 1.4 vid startup and by simply setting the vid to 1.55v in systool was correcting the problem by upping my core 0.05 volts to 1.49.
I have now flashed to official Bios1.5 which has resolved this issue and now the manual startup vid of 1.45 (or 1.49 on my mobo) is applied on every boot.
My opty146 is now stable at 270mhz (NB & SB Link speeds 800mhz) which is near the 272.5 max the bios allows but as im using a stock cooler its running warm under load @54degC so ill stay at this until i see another bios that will convince me to upgrade my cooler to try it
Clocking to 3.0 means i will have to lower the Link speeds to 600Mhz so i cant see any benefit on overall system speed to what ive got now.
Personally i prefer high fsb link speeds and lowering them to obtain a higher htt on amd64 cpu's (robbing peter to pay paul) doesn't make any sence with the exception of some improvement to memory bandwidth. (but this can be altered with divider settings)
btw thats the reason why some ppl are seeing slower 3dmark after clocking the htt but
lowering the link speeds!! - A64's work in a totally different way to intel or amd barton processors where upping the fsb makes a big difference.......owah its Xmas day loggin off have a good one!!