I bought the Streetguard 2 back in April, and I have been generally happy with it. Like you, I'm here in the Chicago area, and have ridden in the mid 40's and the suit was great. The recent heat and humidity have been a bit uncomfortable in the Streetguard, but by no means unbearable. The underarm vents allow pretty good airlflow at even slow speeds. In traffic or when stopped, however, the suit gets warm, but even my old Rukka mesh suit not much better. The Streetguard is much more comfortable than my Aerostitch one-piece in the heat.
If I had to do it again, I'd probably give the Comfort Shell suit another look. From what I've read, it seems to be a pretty good four-season suit (although I typically only need a three-season suit here in Chicago). For now, though, I am happy with the fit, construction and (hopefully) the protective qualities of the Streetguard. It's not cheap, but I expect it to last a long, long time.
Good luck with your decision.
2006 K1200GT - Graphite