Ultralight synthetic jacket

Arcteryx Nuceli is worth a look, not sure how muxh weight it will save though.

Berghaus Vapourlight Hypertherm Smock/Hoody or Haglofs LIM Barrier Pro Hood are the lightest I know of.

I have the Berghaus Smock and it's great.

If you are using a windshirt too, consider a vest as a lightweight puffy option. You can play off the options of the same loft as a jacket while being lighter and more compact, or more loft at the same weight as a jacket of lower loft.

I have an older Patagonia Micro Puff pullover vest that has 100g fill and weighs just 7oz. I can layer that up with ls base layer, wind or rain shell, etc.

I see that REI has the Revelcloud vest on sale for $53 but they dont list the weight.
http://www.rei.com/product/869111/rei-revelcloud-vest-mens#tab-description

Seconding Stephen on the Nuclei, unbeatable warmth for weight in a syn piece. Vastly warmer than Thermawrap, IMO. You might take a look at the NW Alpine Alpha hoody — Polartec Alpha anorak with Atom-LT style side venting panels, so windshirt on top to bring it up to 60gm-level warmth.

Thanks for the suggestions. I did look at the Nuclei, which is happily is on sale right now. I fear it may be a little too warm though.

My system adds or subtracts a borah gear down vest as needed on temps (and for use with quilt), so I don't necessarily need more warmth. Any colder than the two would cover and I would probably switch to down and the precip would then likely be well into frozen territory.

I'll second Evan, the Berghaus Vapourlight Hypertherm (I have the jacket) is a great piece of kit. Warmer than you might expect, and because of its reversibility a much wider range of temps you can use it in.

The Berghaus does seem as though it may be perfect. May be a little short n my long torso, how do you guys find the length.

Also seems very light, around about 8-9oz for an xl sound about right?

Wow. Pricey. My £3 down vest from the charity shop is looking good value. Only 6oz too.

I recommend Climashield fill for loft retention, especially v.s. any Primaloft iteration. If you plan to stuff and un-stuff your jacket many times over its life keep loft retention in mind.

Wiggys makes great resilient synthetic fill but only for their own garments.