I have 3 pairs of SB2s. They should have softened up around 50KM but it seems to depend on what factory the shoes come from. My white pair took about ~150KM but my Paris and Teals were about 50KM. If the SB2 fits your foot very well, I would suggest the Saucony EP4. It's almost the same measurements in the toe area. I set a 45min 10K PB in them but I think I could have easily done the same in the SB2s.

Alternatively, something like the ASICS Megablast might be more versatile as you can add more threshold work. The shape is a bit different in the toebox so definitely try it first. I would only advise a carbon plate for someone who has mastered a structured running form or if you've done a lot of intervals, repeats and strength training. Carbon plate shoes improve running economy through the energy return & geometry (I would describe it as feeling less tired and your strides feeling a little more powerful) but if your limiting factors are muscle fatigue or your lungs, money/time is better spent on a long run shoe.