From my experience, though not great, bike sizing amongst the brands is different....or at least the label they use is. For example, I ride a 52 cm Trek Madone and it fits me great, a 54 Specialized and it fits me great, and a 51 cm Raleigh One Way....you get the idea. Having said that, I would be a little leary of 'fitting' on a 44/48 Specialized and a 52 Trek. That seems to be a little too far off. Go with what feels best to you and hopefully you can get a meaningful test ride to help in that selection process. Let's hope they are not just trying to sell you what they have on hand. Did they do any measuring of your total inseam or anything before putting you on a bike?

P2