A 6600GT is overkill even for 1.6....lets be honest here guys, nailing the 100fps mark in 1.6 isn't exactly difficult.
If you're looking to do it in source, It'd completely depend on the res/options/system specs you've got selected. So give us an idea as to what kind of system this card will be going in, if it's AGP or PCI-E, and what res/effect level you're looking to run it at.
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