Smallest may not be what you want. MJ1200s suck IMO. They dont have nearly the throughput that they could, and FWIW, they barely move more than a MJ600... try it, you'll see. For its size, the MJ600 kicks the MJ1200s butt. You could run dual MJ600s and get a sizable boost over what a RIO800 or MJ1200 would give you.
Smallest? Well... Aquaclear 101/10 is what I use on a nano-reef. It does 80gph only though... too small for you.
If you want something pre-made that smokes a MJ1200, try an oceanrunner. The 2700 should give you loads of bubbles in your bak-pak.