Irvin: 5 starts, 22.1 IP, 5.64 ERA, 20 Ks, 11 BBs, 1.52 WHIP
Peralta: 4 starts, 15 IP, 4.80 ERA, 15 Ks, 5 BBs, 0.93 WHIP
Irvin is far from ready. Kuhl is terrible. The problems Peralta had in his start today (BBs, mostly) are unusual for him. Not a great start, but if he has a couple of starts where he gives up 2-3 runs over 5-6 innings, then he's probably a better option than Kuhl, and Irvin just is not ready yet.
As for later in the year, I'm not sure that Irvin will be ready before Rutledge. Irvin's last start was his first good one since his first.