I'd have though 50-55C with a gorb. You clearly have good case cooling, so it'd probably be a bit below 50C, but I wouldn't expect miracles. The gorb isn't designed for socket A cpus, and a lot of people have crushed their cpu cores with the strong clip on it. With good case cooling and a good hsf like the Globalwin FOP38 or Alpha PEP66 you could get temps around 40C - I'd seriously consider getting a new hsf, cos gorbs (generally) can't cope with oc'ed AMD cpus.
My TB 800 is overclocked to 1000 and it is running between 44 and 47c, using a FOP38 (very Noisy fan though I think that I can get use to it), and cheep grease. I first tried that stupid Super ORB and it ran between 47 and 55c. Without grease it ran at over 63c.
I still havent lapped the heat sink yet, and I am not sure if the artic silver will help much but I am also going to try it.