Well going by the suggested sizing chart on the provided website, 6'1" matches with the 58cm. But again, this is just a stab in the dark. You might have very short legs for your height or some other peculiarity which makes another size more suitable. No-one can tell unless they're in the same room as you and the bike at the same time.
The person you really need to be having this conversation with is the guy who suggested the size in the first place. After all, he's the one who probably fitted you to your Trek, and he should be able to explain to you the reasons why he specified a particular size (since he can see you and the rest of us cannot).
Without him, the only reasonable way you can compare the two bikes is by comparing the geometry. Sizes are just numbers and often don't even relate any particular dimension of the bike.