Although I haven't given up on synthetic sleeping bags, I have given up on gram counting with synthetic bags. The bottom line is that synthetics are bulky and heavy and there's no getting around that. They also have fairly short lifespans. I buy a new one every 3-8 years depending on how much use they see. So I look for a good price on one, make sure it's made by a decent company with decent lightweight materials and just go with it. I don't need a synthetic bag on all the trips I take, but I need one sometimes--typically I bring them for the wet, cold weather that I just don't want to deal with using down in.
My current synthetic sleeping bag is a North Face Snowshoe, which is a 0*F bag that uses a version of Climashiel (though not XP). I don't know its exact weight because I have not weighed it. I think TNF quotes its weight at about 3.5 pounds? I don't really care how much it weighs, though, because that's not the point. The point is, when I'm going on a trip where it's going to be wet, cold, and wet, I want EXTRA insurance against the cold. If that means an extra two pounds so I can have a sound night's sleep, then I'll go with the extra weight. It's not nearly as compressible as down, of course, but it fits in a Sea to Summit XL compression sack pretty well, if that's any kind of reference.