I don't think a road bike is above your skill level. A bike with aero bars, though, is probably asking for trouble. The 850 is a tri bike, but you might not find it comfortable for everyday riding. The Schwinn Letour Legacy is a nicely equipped road bike. As for sizes, they look very bizarre: 38, 48, 54 cm. (Is that 38 a mistake?). The top tube length is also useful number. The standover will tell if the bike is too big. You should have 1-2 inches between you and the bike. The Schwinn small has 735 standover and you measured 740. That's 0.5cm which is pretty close.

The proper size of bike is one where you have adequate standover, are not reaching too far, the seat is not too low and not too high (look at pics and you'll see that people typically have 6-12" seat post showing). I think that 20" Trek hybrid is too large. I am 5'7" 31 inseam and I purchased the 17.5" and the seat is quite high. The general wisdom say if you are between sizes, purchase the smaller size.

Slim's advice seems OK. Or you can continue to shop around.