First time poster here, hope you guys can help me out.

Due to hip pain and an operation last year I have picked up cycling and am happy I did. I am now looking for a 2nd bike for longer endurance rides. I have some issues with frame size and even after spending hours on the internet and talking to a bike fitter I am unsure which size I should get. Problem is I have an inseam of 90cm and a height of 183cm. Going by inseam alone I should ride a 58cm frame which is way too big. Going by the fit calculator at competitivecyclist I should ride between 54.1cm and 54.7cm horizontal top tube length. The bike fitter I talked too said the same. He measured me on an old frame 2 years ago which had a top tube length of 56.5cm and said I was too stretched out. Even after shortening the stem from 110mm to 80mm he said I should consider a 54cm for my next frame.

I am currently riding a Canyon Inflite 9.0s in size M with a top tube length of 55.3cm. I am happy but have neck pain on longer rides and it seems my reach is the problem but it could also be the saddle to handlebar drop. The new bike I want is the new Cannondale Synapse. But the million dollar question is, should I go with a 54 frame or a 56? The 56 would be even longer than my Canyon, but the stack would also be higher. The 54 would be shorter, but the saddle to handlebar drop greater. I rode both of them and the 54 seemed small handling wise. But just because the larger one felt right on a 2-minute ride, I don't know if I would say the same after a 4-hour ride or longer. I could get used to the handling probably, but I really want to get rid of the neck and upper back and shoulder blade issues.

I can't post a picture until I have 10 posts it seems.... bummer....