I am in the market for a new PC but am confused by all the different intel processors. Its obvious some retailers are using lesser processors to cut costs. I was wondering if someone could put them in order for me. Is there a general rule? Thanks

Corei5-750 2.66GHz
Core i7 860 2.8GHz
Core i3 540 3.06GHz
Dual Core E5300 2.6GHz
2 Duo E8400 3.00GHz
Dual Core E6300 2.8GHz