I am really curious to try ss/fg and seriously considering the salsa caserroll single especially because if one gear doesn't suite me I can switch this bike to geared. Are there any other frames/bikes that are similar in this aspect I should also be considering? I am familiar with the crosscheck but already have 2 cross bikes and really want to go with calipers on this one.

Just about any older road bike has horizontal dropouts.

Yeah I should of mentioned I am trying to stick with new.

i think masi had one with convertible dropouts. forgot the exact model though.

The Masi Speciale Commuter.