I have an Athlon 64 X2 4600+ on an Asrock ALiveSATA2-GLAN.
I've read that the 4600+ can be overclocked quite easily on stock cooling but I haven't tried because I don't need anymore out of it
I have recently read a post where someone is running their 4000+ at 3.0GHz and it's stable. You might want to try asking here: http://forums.overclockers.co.uk/
Which 4600+ are you running? Windsor? Brisbane? Whats' the L2 cache?