You are tall enough to ride a 29er, don't let the salesman fool you. I am 5'8" and ride a Monocog 29er. 29er's are mostly marketed to XC guys who tend to not ride as hard as dirt jumpers and downhillers though. I would recomend you get a replacement deraileur hanger to carry with you if yours is replaceble. A chain tool and SRAM power link or two is a good idea too. Mountain bike wheels are pretty tough, but if you start destroying those, look for something marketed towards dirt jumpers.