I'm not sure about the superorb versus chrome orb perf. difference, but regarding artic silver versus the Phase-Change Thermal compound on the heatsinks, it would depend on the situation.
If you plan on removing the heatsink, playing around with other heatsinks, etc. You're probably better off with Arctic Silver. it performs better than the PCTC, but is harder to apply, whereas PCTC is fool-proof.
If you plan to install it once, cook the compound so it melts, and then to leave the heatsink on, the PCTC is a more than adequate solution. It should perform significantly better than radio shack/and other silicon-based thermal greases, and not run the risk of drying/cracking over time(due to the high heat of duron/t-bird's).
Mike