Honestly, if you feel it is at the limits of your comfort for standover height, then it is probably the right size for you. Still, I am pretty sure it is not too big for you.

I like a big frame and at 6' I prefer a 25" frame, although the difference between the standover height and my inseam is perilously close to zero. I rarely start or stop standing over the bike and when I do I just lean the bike to one side.