the only difference between retail and OEM is the inclusion of a fan in the retail boxed version.
Retail CPUs also come with a 3-year warranty; OEM CPUs are typically only 30 days. Some retailers offer up to a year warranty on OEM CPUs if you buy a heatsink with it - but that's through the retailer, not the CPU manufacturer.
I'm guessing the fan I'm running on the 2100 would be sufficient. I never found the retail fans to be all that great so I put my own on.
Retail heatsink / fans are generally adequate for regular use; you usually only want a third-party HS if you plan to overclock and/or your case gets pretty hot inside.
I personally always go with retail CPUs, largely for the warranty: the cost difference is often negligible; and while I've never held onto a CPU for a full three years, I think 30 days is much too short a warranty. I see the retail heatsink as a freebie.