OP, I didn't see where you mentioned your leg length. If you have close to average body proportions, the 58cm frame should be about right for you at 5'11". If you have longer legs and a shorter torso, you may need the shorter top tube you think would be a better fit.

The suggestion Salamandrine offered about using the Competitive Cyclist online fit calculator is good advice.

The chart below will give you a "sanity check" to get you in the ballpark. It assumes traditional geometry like your Sirrus has, and the seat tube measurement is from the center of the BB spindle to the very top of the seat tube where the seatpost is inserted. Measure your leg length as shown in the Competitive Cyclist photo below.