Pay no attention to the length of the seat tube, especially on a compact geometry frame. It's the top tube and head tube lengths that will determine if the bike fits. A large OCR has a 58.5 top tube and a 19.0 head tube, per the geometry chart: http://archive.giant-bicycles.com/us...&modelid=11330
I have fit riders of your height to 60 and 62 cm Treks and 61 cm Specialized road bikes, to give you an idea of the range of sizes that might work.

Giant also has a fitting guide to their compact frames on this page: http://archive.giant-bicycles.com/us...50.600.100.asp. According to this, you're at the upper limit for the large. And if your body proportions tend toward long limbs, and your flexibility and core strength are good, I'd even recommend the smaller frame. In any case, though, you might have to experiment with longer stems. An out-of-the-box fit is quite unlikely.