yes.....very few don't see improvements from multiple card solutions. A persons only threat is driver support if they are using multiple card solutions but driver support has gotten fairly good these days and even those benchmarks show promising signs considering the card just came out when they did those crossfire reviews and the scaling is phenomenal.
I would personally go with a single fast card also and CFX/SLI it but its pricier.
I hope to just get a 5970 when theres a huge price drop. The XFX 5970 Black Edition looks insanely sick!! Volt-modding software and all that, plus they are handpicked and the website says they are meant to get 1000mhz core clock and 6.0GBPS memory clock.
http://www.fudzilla.com/content/view/16486/34/
and
http://forums.amd.com/game/messageview.cfm?catid=233&threadid=123050
this guy said he talked to staff member and they are binned to overclock atleast 1050 core, 1450 memory with voltage increase that comes along in the software provided only for the black edition. Sapphire also has one that only works with the sapphire OC model supposedly so this voltage tuner seems to be exclusive.