I was in the same boat a while back... and ended up getting a notebook with the x600. I benchmarked both.. and my x600 was significantly faster, but they were comparable... of course, my processor speed went from an athlon 64, 3400+ to a 4000+ and videocard memory went from 64MB to 256MB. Im sure the better specs affected the benchmark as well.
Main: i7 970 at 4.0Ghz, Asus Rampage Extreme III, 6GB Corsair XMS DDR3 (3x2GB), 240GB Intel 520 SSD + 300GB Raptor, AMD 6970 , X-Fi Fatality, Killer NIC 2100, Corsiar HX 1050W
Secondary: Core 2 Quad 3.0Ghz, 4GB Corsair XMS, 160GB Intel SSD, ATI 7770 Ghz Ed. , Antec TruPower 650W
Laptop: i7-2670QM, 8GB RAM, 160GB SSD , AMD 7690M