For dress shirts I usually do 2 things. I get mediums, never tuck them in and roll-up my sleeves (this is my preferred method). If I want my sleeves to actually look like they fit me I get a large and once in a while I get it tailored, if I don't tailor them it's because I usually wear that shirt with something over it like a sweater/vest/blazer/jacket/etc so it hides the bagginess around my back/waist area.
I would really like to pre-order this but I actually don't see any examples on their site of what their different sizes are and how they'll fit. All I see is the same model type. You can tout that you are going to have all these amazing different sizes for all types and not showcase that. I'm particularly looking for someone of my body-type.