Tom,
In my opinion, it's more about the peice of maple, than purpleheart Imo, the purpleheart doesn't touch the pin, or the shaft, so as far as hit goes, I don't think it make's alot of difference, but as for balance/weight distribution, it's Ideal. You like a 18.50-18.75 ounce cue correct? Purpleheart would help get that, I try to make most of my cue's weight forward, and this combo of sneaky easily allows me to do just that.
Now before every one chimes in, I don't care to core my cues (although I will if needed or requested), Bacote is another good one.
Bryan