Either 54 or 56, but how do you tell?
Well, if you're built like most German with long torso and shorter legs, then you'll ride a 56. So, if your "6 pack" abs are more like 8 or 12, go for the 56. Also, if you have long arms. Scott, Giant, Canondale, Specialized
However, if you're the other way around, like most French, with short torso, possibly shorter arms, and long legs, then you'll ride a size 54 with a Profile Designs H20 performance centric riser stem sized appropriate for your reach. Trek, Schwinn, Look, and Specialized Roubaix
The easy way to figure out which one you are is to try on men's collar shirts (traditional shirts for suits). They come in two arm lengths. Shorter sleeves rides the short bike with a tall stem. Longer sleeves rides the larger bike.
Ignore your pants, inseam, and all leg measures unless you are shopping for 20 year old bikes. Standover height is an unreliable measure on the modern compact frame geometry. Refer to the epic length seatposts as seen on the Tour de France. Those are compact frames, and so are the majority of bikes at the bike store. Normally, one would only show THAT much seatpost to fit a hybrid, but it was a good example, wasn't it?
However, there's no text answer that can stand up to a comparative test drive, which is what you need to do. Just test drive until you find the one that stands out as a lot faster and a lot more comfortable--at the same time. That indicates fit.
P.S. Your traditional size might have been a 58, but please avoid a new 58 because it could cause you spine damage from overreach, and would certainly be a short distance ride. Look at 54 and 56. With "lettered" sizes, ignore the numbers entirely and go by test drives.
It is best to test drive bikes when your tolerance is low, such as after work or after pulling weeds in the garden, or after you have already been on a 75 mile ride. With a low tolerance (tired, aching) when you begin your test drives, spotting the "one" that combines comfort + speed will be even easier.