ehh im not sure about 2008 geo. but im 6'3 with a 34-1/2 inseam and i just put money down on a new 2011 flash 29er and man that fit me pretty darn good im gonna go on a limb and say go get the med. im no pro and my personal taste for a 29er bike is to ride a size smaller for some reason i just dont like the big truk feeling i get when i ride an extra large 29er i just like them a tad smaller it give the bike under me a more flickable feeling. like i said its all personal preference but on a normal basis and youre size im gonna have to say med.
ive got a 2008 jamis 26 inch bike in extra large. ive never been able to ride anything smaller in a 26 inch bike. a 29er opened up a whole new (and better) world for me. the new 2011 c'dale i just put on layaway is my 2nd 29er.