I would run my toons from RFC through SM with my Hunter and Druid (alternating for variety). If you can kill fast enough, the exp is better than grinding. It goes even faster if you ignore loot.

I'd set the pet to agro, and then poison about 10 mobs, let them run to me, and hit a fire (or snake) trap. Repeat. With my Druid, I'd go bear form and just spam Swipe. I'd crit so often, my rage bar would be full most of the time and it would keep me healed (feral spec). I timed SM cath runs and found the Druid to be *slightly* faster than the Hunter.

You want the mobs in the instance to be red con. And you'll have to place your toon in a safe place, as the red con agro range is HUGE and you can't use the /follow command without the alt dying.

After SM-Cath, your 70 can't kill fast enough to make it worth it. But you can still run the instances to get good gear. I would run my melee toons especially, as they kill faster with blue weapons.