Need some sizing help
 

I need some sizing help...and unfortunately the numbers aren't adding up for me and there's no bike shops in my area that carries this bike. I am looking at getting an Empella frame but am confused. Here we go...I currently ride road bikes with a 54cm TT, my current cyclocross bike which fits me PERFECT and is currently what I"m using for a sizing reference is a 50cm Cannondale Cyclocross with a 53cm TT and about a 54cm ST c-t. I had a 50cm Redline Conquest which I sold because the TT felt a bit too short and when I stood over the TT I had absolutely no standover room, this had a 52.5cm TT but don't remember what the ST was. The 52cm version with a 53cm TT felt way too big when I first tried it out, was almost on my tip toes when over the TT. So I"m wondering what size I would need for an Empella, I wish I could try one out but don't know anyone in my area that carries them and even if they did they may not have my size. Anyways, the empella 55cm has a 53cm TT but a 55cm ST which I'm thinking may cause some problems. The 54cm has a 52.5cm TT. It's an expensive frame so I'm trying not to do too much guessing but unfortunately Empella's website doesn't list any head tube/seat tube angles or any other information in helping me to compare it to my cannondale. Any suggestions would be much appreciated. FWIW my height is 5'7"

Thank you,
Dave