Heat Spreaders on RAM and CPU Question?

I'm planning to buy a PC from ibuypower and one of the RAM options is corsair/mushkin with heat spreader. What is the performance improvement if I do get the Heat spreaders?

Also, Which RAM is better, Corsair or Mushkin?

Thanks for the quick reply. I don't plan to OC so I can save $50.

I also have a question about CPUs. I'm planning to get the E6750, but the E6850 is offered for $90 more. The E6850 is 3.0 GHz instead of 2.66. Would it be worth it to spend the extra money on the E6850?