Joined: Aug 2011
Posts: 2,185
Likes: 2
From: Canada/604
Bikes: Giant Defy with Dura Ace group, & Ksyrium SL's,Specialized Allez Shimano mixed/mashed,2011 Opus Sentiero,2008 Kona Jake the Snake,Custom built track/fixed,Stumpy Hartail,Kuwahara/ET bike.
Pass on the GMC, it's not worth upgrading. Upgrading a bike gets expensive quickly.
I'd save up enough to double that $300 dollar budget to the $600-$650 range, your options will be a lot better @ this price point.
If you need to pay a shop to assemble the bike for you, be prepares to spend a few $100.
Good Luck finding the bike you need/want.