XFX 4870 Heatsink Woes - Fan Replacement Q

I have a XFX 4870 1gb on the way. Should be here tomorrow. I picked it up for $142 shipped brand new, is this a good deal? Here is a link to the card (not where i bought it from):

http://www.newegg.com/Product/Prod [...] -_-Product

After I ordered, I realized this is the revised card with the "poorly" designed heatsink (or so they say) that dumps hot air into the case. I was thinking of taking off the plastic shroud and installing larger 120mm fan (or 2) using zip ties. Has anyone does this before? Would this void the lifetime warranty?

just use rivatuner to raise the ran rpm speeds or set it to auto from there?

I have good airflow, I am merely concerned about the heatsink on this particular card not being effective...