I'll tell you I rode both,51 and 54 first I said this is bike maybe too small they told me that Orbea Geometry is a bit different than other bikes and blah blah blah then I rode the 54 again and honestly was kind of big,I've being riding my 51 for some 7-8 months now and fits like a glove,I can go 80 miles and feels like butter and turning is amazing, I know the bigger the frame the worst to handle specially when you are 5.9" but is up to you,as a matter of fact in the near future I will put together another bike and will be on a 51 Opal frame,but in any case you will have a heck of a nice bike,I see you have Ultegra I hope is the Ultegra SL group.