Whyte Suffolk / Dorset Frame Sizing

uk.kv

Hi all, hoping for some owner feedback, I've narrowed down my winter/all weather bike as the Whyte Suffolk, I'm 5ft9 with normal proportions the spec guide says I'm a 54 size frame (5'6 to 5'9). I'll be buying from my LBS, they have this model in the shop and the helpful sales guy tells me it fits with me sat on it however it feels a tad to big, unfortunately they don't have a 52 in shop to compare, so I would need to order it/buy it and hope the 52 is a better fit, of course I'd rather avoid any drama and hoping any owners out there can give me feedback on sizing.
many Thanks, Kev