I am looking at a Salsa El Mariachi size Medium. I am wondering if it is the correct size for me. I am 6'1" and have a 32 inch inseam. When it comes to road bikes I usually ride something w/ a 58cm-59 top tube w/ a stand over just shy of 34". How do you correctly determine sizing on a 29er?

Hm, I'd tend to think you'd fit better on a Large.

Just finished test riding a M and L size GT Peace. I'm 6-2, with 32" inseam pant length, so a longer torso. While the M felt good as far as "quickness" , I was too cramped in the cockpit. After 10 minutes on the L, discovered it's a much better fit. Btw, I ride the same size as you in road bike. A ride will tell you lots.