Keep the HT at 2000 +/- 100MHz. Over clock your ram. You wont need to overclock you CPU-NB unless you put faster ram in there. Id look at getting some decent 1600MHz Ram and overclocking the CPU-NB to around 2700MHz. Will take between 1.3-1.35 Volts.
Your CPU should go higher depending on your cooling. 4GHz at around 1.45 - 1.5 volts should be possible. Keep volts below 1.55 and temps below 62 at full load. Use prime 95 blend test to test stability.
is a great resource for Overclocking Phenom II.
THe 955BE and Phenom II in generall are great overclocking CPU's and very tolerant of beginners. Have heaps of fun.