core number vs speed???

[gamblor]

maybe someone here can shed some light on this.
getting ready to upgrade my mac.
hearing conficting stories about clock speed vs number of cores on the mac pro.
seems like the single processor machines are clocked significantly faster than the dual processors. ex., the single processor 6-core can clock around 3.33ghz while the dual quad(8 cores) clocks around 2.4ghz.
which, if any, would be optimum for protools HD?
does PT even takes advantage of multiple cores yet?
looks like the only def advantage to the dual proc's is the extra memory slots, 8 vs 4 on the singles.
this move is going to cost me a large chunk of change, so i'd like to make the right choice and hopefully have a mcahine that's going to last more than a couple of years before it's outdated.
any info would be awesome.
thanks in advance...