The rab xenon has been a great piece for me going on almost two years. Its not as warm as it once was and its held together by gorilla tape at this point, but I'd still say its warm enough for what I use it for (summer backpacking, bc skiing, rock/ice climbing--intermediate layer)
Its a very warm and weatherproof jacket for the weight, especially when it was new. The newer version of the xenon ads a couple oz, so consider looking for the discontinued model.
If I were getting a synthetic piece today it'd be the arc teryx nuclei hoody or the mountain hardwear thermostatic hoody (fall 13 model), both about 10oz. Tried both on, and I'm confident either would suit my purposes well. The arc teryx especially with the non-stitchthrough design (better wind resistance). Wonder how the shell material compares to the xenon.
For a three season synthetic piece, I think a 60gram primaloft hoody around 10-11, is a good bet. I have a lightweight, but much warmer down hoody that I can pair it with when it gets truly cold.