5'7" 30.75" inseam.

I sat on some treks today while I was in there for my bike's free checkup and found that my terrible shape has me stuck between 52 and 54cm frames. I have a very long torso and very short legs. The stand over on the 54 was more than enough in practically flat sandles so I know i'd be fine in my duck walkin' shoes. However the saddle was all of 4 inches above the top tube and the reach to the pedals was very long. The reach to the bars however was perfect and I was very comfortable. The 52 felt cramped, but the saddle didn't need to be completely slammed. To compound this problem I'm considering purchasing a frame set and building it myself as my budget would be much happier with that than 2k outright, but I have no clue where I should be at.