They only difference is the 165 has up to a 9x multi and the 170 has up to a 10x multi. If you feel the 10x multi is worth the extra price, then get it instead.
OEM dosn't come with a heatsink and fan, and it only has a 1 year warrenty. Retail comes with a heatsink and fan and a 3 year warrenty. But the warrenty dosn't matter because as soon as you OC it the warrenty is void.