The Trek 820 is on the low end of trek's line, and is aimed at entry level recreational riders. As such, it's geometry is set to put the rider in a much more upright positon (ie. shorter top tube) - good for comfort, bad for performance. Also, Trek measures their frame sizes from center of BB to top of seat collar, while most other manufacturers will measure to the center or top of the top tube. My standard advice when selling bikes is that fitting the cockpit (saddle to bar distance) is much more important than standover. this will determine your weight distribution on the bike, and how it will handle for you. If your weight is too far back (to short of a cockpit) the bike will be a poor climber, and have a tendancy for the front wheel to wash out in corners. If your weight is too far forward (too long a cockpit) the bike will be hard to control in technical terrain and tight singletrack, and will give you that over-the-bars feeling on downhills. Anywho, a bit more info would be helpful - how tall are you and what is your inseam length? What size stem are you currently running on your 820?