Seat tube length is pretty unimportant.

What is missing in the responses is acknowledgment that the OP is buying a touring bike. Touring bikes do not use the fit geometry or road racing bikes, and often have shortish top tubes compared to racing bikes of the same size as they are intended for a more upright position.

If the OP has a model in mind, please post it. Otherwise it is hard to say anything definitive about fit on a touring frame.