I have been studying the belt drive area quite a bit. A great resource for information and an on-line calculator is www.brecoflex.com. I would look carefully at the AT style belts, the special teeth version to minimize backlash, and possibly the information on trolley arrangements. The on-line calculator is great for belt selection and force requirements.
A some what not so obvious item to belt drives is the increased radial load that is placed on the stepper motor bearings, and the increased sensitivity of the design to stepper motor shaft / bearing tolerances compared to screw drives. There actually are not that many brands of motors that specify substantial radial load and tight tolerance. Interestingly, some of the better ones appear to be from Kelinginc, which has a forum section on cnczone. Take a look at their higher end nema 34 size motors data sheets, as well as anaheim automation's 34 R series and pacific scientific 34 size motors.
About 1/2 of my postings on cnczone have been questions or information about belt drives, so if you are interested, you can search my posts for a real newbie learning about belt drives, and the very good responses from others here on the forum.