54 or 56 bmc team machine

Currently ride a Scott cr1 in 54 (medium) I’m 5ft 10.5, 32″ inside leg, my current bike feels ok but slightly cramped, I think I’m at the top end of a medium size or just at the low end of large if that sounds right? This is the next bike I’m looking to buy http://m.evanscycles.com/products/bmc/teammachine-slr01-dura-ace-2014-road-bike-ec052717

I’ve been told a more stretched out position is better, but will it give me less options to adjust the fit, what’s most important, reach, stand over clearance etc? I’ve got a test booked in at evans on both sizes, what’s important to consider in making my mind up? Any help or advice will be greatly appreciated