I know what you mean, at 5’9 I preferred the feel of last years 51cm over the 46 which was far too short imo. Standover was the killer though.
For 2013 they’ve improved the clearance and the sizing, 51cm has become 49cm (I think), which is closer to being workable for me. If you’re relatively long legged you might get on much better with the bigger size, especially when fitted with the shorter stem the bike needs. Having said all that though, they’ve increased the TT length of the smaller sizes too and having tried them, it is an improvement. However I still find myself struggling to get a good fit on a lapierre.