You can cut a slight amount more gems per hour then bodies you can craft (I believe it's 4500 gems/hr). Cutting rubies is roughly the same exp/hr as crafting black dragon hide bodies, of course diamonds are faster and then dragon stones are roughly 600k exp/hour. If you're going for max exp training crafting over this double exp weekend; rubies are less expensive than training crafting with black dhide bodies (when I looked into them, rubies were ~8 gp/exp and dragonstones vary from 20 gp/exp to 5 gp/exp and yes, they are buyable in bulk).