I have the same height and inseam as you. I would go for M/L assuming the geometry is similar to the Contend with the 56cm virtual top tube. If you do that, then also cut the fork a little longer and put more spacers under the stem. I also like a 140mm stem so that or perhaps a bit longer should do it for you. My Ridley has a 56.5cm VTT. So its only 5mm longer and I use the 140mm stem on it. On the Supersix Evo, I'd probably get a 56cm.