Years back (2002) when I bought my Lemond, I had to choose between a 51 cm and a 53 cm... I choose the 51 but wish I choose the 53. I'm 5'8" and am evenly proportioned. My legs are not short but neither are they long like some women and I have shortest arms so I was afraid of my reach and being able to access the brakes and shifters. Of course then I rode more upright. Probably, if the store had one, I would have purchased a 53 cm WSD bike, but alas I did not.

I've now been able to get into a more aerodynamic positioned and have lengthened my reach considerably. The 53 cm would be just right but every bike is totally different. Some (like the Lemond) have longer top tubes, some shorter. Bikes are measured differently.

WSD designs generally have shorter top tubes. A 50 cm WSD bike should have you sitting nearly upright. Is that what you want?

I would really ask him to explain why such a discrepancy between the two measurements. The 50 cm WSD sounds awfully small... like the shop has a bike it can't sell and they found a pansy.

Best thing to do is spend $100 and have a proper fitting and then find the bike that fits the recommendations best. Good luck!!!