Bought a Bike Today: Fit Question

I am between 5' 9" and 5' 10" and transitioning from a mountain
to a road bike for the very first time.
I am looking at a couple of bike's at the Trek superstore and
have the choice between a 56" and a 58" frame. On the 56", it's
a tad crowded in the leg area when riding--but not much. But
the reach is *perfect* for the handlebars. It's spot on perfect.

On the 58" the reach is a tad too long, just so it's noticeable. There's
more room in the leg areas because of the larger frame.

The sales guy says I'm a 'tweener' and if there were such a thing as a 57"
frame, that would be for me. My wife thinks the 56" looks a little small
beneath me as I ride, and that the 58" appears more natural--but admits
that like me she knows nothing about how a road bike should look or fit.

So, for long-distance riding--which is what I tend to do--do I want the slightly
better leg room or the slightly better reach/grip?  Do road bikes typically look
a bit smallish beneath riders?  The salesperson has recommended the 58"
after a fitting and whatnot. But after riding it for a while--I am not convinced.

I am free to return the 58" anytime.

If anyone has a suggestion, feedback or input it would be wonderful to
hear your views.

Thanks, Breunor.

I've taken a few more trips and have, I think, improved my riding
form so that the 58" seems to be a good fit.  It's difficult to know
absolutely for sure.

The sales person's opinion is that the 58" is something that I can
grow accustomed to and stretch into as I get used to the form, but
the size of the 56" is much more limiting in terms of how I can "grow
into", or get accustomed to, riding a proper road bike.

It's one of those things I guess I'll never really know for sure.  But you
are absolutely right: if after another day or two I'm not satisfied I'll
go back for a better fit.

Thanks for the comment.