Do yourself a favor and ignore frame size numbers. Concentrate on the numbers that affect your position. Companies like Trek, Cervelo and C'dale all list the reach and stack values that tell you almost everything you need. The only thing missing is the seat tube angle, that affects how far back the saddle can be moved and how much seatpost setback you might need. If there are no reach and stack values, you have to rely on the next best thing - TT length and seat tbue angle work together to define the reach. The head tube length, with the headset, can be used to compare the approximate vertical stack, but watch for significant differences in the BB drop. More BB drop reduces the required head tube length.

You could probably benefit from a preofessional fitting - not a bike shop guy trying to sell you whatever bike he has on the shop floor.

A fitting always starts with setting the saddle height and setback and that's where the first mistake usually occurs. A plumb bob is used align the knee over the pedal. That's OK as a starting point, but not something magical that can't be changed for the better. Quite often, a further back position is more desirable, to minimize the weight on your hand and achieve a better balance over the saddle.

When trying to communicate your fit, post you acutal saddle height, measured along the seat post centerline, the saddle to bar drop, the amount that your saddle nose is setback from the BB centerline and the diagonal distance from the saddle tip to the center of your handle bars.

Never expect to just get on a bike and have the proper stem length or handlebar height. Those both have a lot of possible adjustment.