Question about standover height and sizing

[gocard]

Hi everyone! I have a question about standover height and reach. I'm about 5'5" and about a 29" inseam. I test road the WSD Cannondale Synapse in a 51 and a 48. The reach was fine for me on both bikes and the 48 clearly had better standover clearance. However, I liked the 51 better - it felt more comfortable to me while riding but my seat needs to be lower.

I wasn't sure if it was my imagination, but the 48 seemed to have a much more sloped top tube vs. the 51 and it looked a lot smaller and I didn't like the appearance as much. Is it silly? I feel more comfortable riding on the 51 but technically the 48 is a better "fit". What should I be going for? I wish there was a 50! Thanks for your advice!

**edit** I did a search on the forum for standover height but haven't found much that helps my quandary. If you know of anything please pass it along! Thanks