I have an Arcteryx Beta AR that I love. Just recently, I looked at replacing it with something lighter. I bought the Sirrus SL from REI outlet.
HOWEVER, when I got the Sirrus, I promptly returned it. First off, the fit wasn't perfect. My Beta is a L which fits me generously enough to layer, but still doesn't look "too big". The Sirrus in a L (the only size on sale) was a bit to large. I think a M would have fit better.
Second, it weighed in at 14oz, only 6 less than my Beta. That, in conjunction with the fact that my Beta is in perfect shape and wouldn't cost me $175 led me to return the Sirrus immediately. It also didn't look like it would hold up nearly as well as the Beta that I have.
Here's what my ideal layering system would be if I had the money for it right now: I'd get a nice softshell jacket and then a light hardshell (probably a sirrus) to wear only when things get really nasty. I'd have less problem carrying a less durable shell when I know that I have a softshell that will handle most everything.