Pleas! Help with sizing! I seem to be all over the place!

[Marubex]

I am looking into getting my first road bike as I want to start doing triathlons. I have ridden hybrids and mountain bikes in the past. I am having a hard time figuring out the sizing, since most LBS only carry one or two brands each seem to be pushing what ever they have available, from 47 to 51.
Here in Mexico prices are a bit higher so here is what my budget allows, and testing is very limited, just a little trip down the block.

In Trek a 47 I got toe overlap and they tried to push it, but I tried the 50 and felt much better.
Trek Lexa $929
Trek Lexa SL $1152 this is a 2014
http://www.trekbikes.com/us/en/collections/womens/road/performance_race/lexa/

Giant Avail 3 in a XS $915 I feel like there is stand over clearance even if I actually have it, i can lift the bike about two inches from the groin before it hits my crotch, but it feels as if it was less on mount, I don't know how to better explain it.
http://www.giant-bicycles.com/en-us/bikes/model/avail.3/18778/76125/#specifications

Specialized Dolce S in 51 felt ok, but I think it is overpriced for what it is $1457
Specialized dolce $1020 the only one with aluminum fork of the list
http://m.specialized.com/us/en/bikes/womens-road/dolce/dolce

Orbea Avant H60 in 47 $969 somehow I do not have toe overlap in this as opposed to the Lexa 47, I guess different geometries. I haven't been able to ride this one yet, but I seem to have good reach. It is made in Spain and has lifetime warranty, has been building bikes for more than a century. Not sur what the fork is made of.
http://www.orbea.com/gb-en/bicycles/avant-h60/

How would you choose? Or which would you choose?
Being new to this i am rsluctant to spend much, but want something comfortable and good enough, that would last me for a while. And if spending a little bit more would make much of a difference?

Thank you so much for your help

Maru

[Crankin]

Yes, I almost went nuts navigating the Trek site, trying to find the geometry match from the bike I rented on my tour to a 2015 version. It took hours of work. Then, I had the LBS owner confirm this by looking in the "big book" that Trek gives to shop owners. It was worth it, in the end, but I am not sure why they do this. You would think they would want to make buying easier!

[Crankin]

I agree, go for the best components you can afford. I got rid of my first road bike after a year because of the poor shifting of the Tiagra/Sora combo (which was then the lowest) and upgraded to Ultegra. It was worth it. I never could shift into the big ring on the triple of my first bike and it always was having issues jumping from cog to cog. That is not good for a fairly new rider. And yes, Trek does have it down for petite female riders. So does Specialized, but they do not have as many options.

[OakLeaf]

I would wait a few months to make sure you have the correct stem length before you invest the money. A carbon seatpost is also a good idea. And that can be done right away.

I might not upgrade the seatpost right away either if you're taking some time to get the fit dialed. You might wind up wanting more or less setback than average.

[Crankin]

Oh, I know that, Murienn. I fought DH about getting a combo of 105/Ultegra for my Guru, but it's clear the 105s have been upgraded. It was the only way I could get the shorter reach shifters (which were still not quite short enough!).