how about just try some bikes that are different sizes and chose what you like? especially as you get older youre going change what will fit you comfortably.
what specifically you feel isnt a good fit between you and the 60cm frame? too long when seated? too long when standing? top tube too high and you wish it would disappear?!I'm a little hesitant to do that because the frame I've ridden for the last 2 years is obviously too big for me (5'9", 60cm frame) but until I had ridden for about 2 hours in a single ride I could have told you with complete sincerity that it fit me just fine. I've done several 3+ hour rides, and one 8+ hour, and I can now say confidently that it's the wrong size. I could probably pick up quicker on those clues now, but I don't know how quickly.
closer to the ground and therefore more confident you say. this pic is 70mm bottom bracket drop and common. maybe your bottom bracket is lower. maybe you mean youre more elongated and in a racier position when youre "closer to the ground". what do you mean closer to the ground?To long seated, mostly. I notice on the smaller (54) frame I'm also closer to the ground and therefore more confident on rougher surfaces.
a lower seat tube angle, or higher maybe would be the right term, wont bring you lower to the ground really assuming you end up with the same saddle height. I like a very setback seatpost and big angle on the seat tube as it puts me in a more relaxed position and even enables me to lean farther over and not have more weight on the bars.I think most of "closer to the ground" is a lower seat tube angle. On the larger frame I also had my handlebars set higher than my seat.
Rough surfaces would be light gravel.