I think O2 and Frogg Toggs stuff runs big as the fabric won't stretch and might tear if stressed. You get some "bellows effect" ventilation too.
I think this class of jacket is good for those climates where rain is rare or short duration, and for summer CYA when rain isn't forecas, but I wouldn't plan on wearing one for days on end. I keep a flat pack of 18" duct tape in the pocket.
There's no free lunch or miracles on rain gear. Typically, high budget fabrics will come with quality construction and hardware, and a warranty to suit. Any unlined interior coating is exposed to wear and delamination over time (warranty time again). Any of the super light shells will be more fragile and subject to wear from inside and out, as well as attack from sharp stuff on the trail. I look for lots of venting and "tough enough" fabric. That leaves most of the 2.5 layer jackets with pit zips and weights around 12oz.
If you want 5oz and no venting features, you are relying on the fabric coating and the front zipper for breathability. The lighter fabric and coatiings will take a beating from your pack straps inside and out. IMHO, the light coated jackets are just a sweatier version of a windshirt.
You can pray, hope, scream and cry, but there ain't no miracles, yet. We'll hear about it when it happens :)