8020 3060 extrusion weighs 7.462 lbs/ft. CRS .25" x 2.5" is 2.1525 lbs/ft. Assuming a 5 ft long gantry you're talking about roughly 60lbs.
People drive these gantries all the time with 300-400oz motors with no real issues. Considering you're doubling the weight of the gantry but also doubling the torque of the gantry, I can't see you having an issue. Obviously 1200oz or 1600oz motors are also available for not much more money. You just have to be careful about what the torque curves look like.
You might want to contact the builder from this thread: http://www.cnczone.com/forums/cnc_wo...x8_router.html
His gantry is just as heavy if not heavier and he could probably give you a review of the package he bought and whether he would do anything differently.