I love your blocks. For me, while I like the look of both ways, the wide look of the sash/border distracted my eyes from the beautiful block. If it were me, and I chose to use the border, it would be a very narrow strip. As suggested by others you could always do one floating and narrow sash with for the other. I wish you a lot of luck deciding. It's going to be lovely with those blocks for sure. I hope you show the end results when you're finished.