well if it were a q2.4 vs a d2.53, then i'd say no brainer, go for the quad, at 2.2 vs 2.53 i'd say wait and see, at 2.0 vs 2.53, i'd say go for the dual core. Having just looked up the Q9000 i'd say no, the Q9100 i'd say maybe. But and its a big one, all of the core duo mobile processors max out at 34W, the Quad is 45W, so can the thermal solution cope?
I think the heat would not be a problem because i have taken some extra measure to keep the laptop cool. The only problem is i dont know if the socket type on the q9100 is the same as the q9000. I have an Asus G72GX.