Looking at metal hardware( cap brackets for posts to beam connections) for my porch roof project I see a lot of the galvanized hardware (G90) stating "not for use with treated wood " While the exact same thing in G185 triple zinc for treated wood is 3 to 4 times more . If I paint or coat the steel creating a barrier between wood and metal could I get by with using the cheaper galvanized brackets ? All hardware will be under a roof out of direct rain and snow. -Thanks

Someone in construction might have better advice on what results the G90 would give you long term- here's my advice from an engineering perspective:
You're dealing with more than weather elements:
Most pressure treated lumber is now treated with Alkaline Copper Quaternary (ACO) and Copper Azole (CA)- Corrosion occurs from galvanic reaction between the hardware and the chemicals used in the treatment process. Think of a battery- corrosion occurs when two elements that appear further apart on the periodic table don't get along.The difference between G90 and G185 is the amount of galvanized coating or protection placed on each side of the hanger or hardware- usually expressed in .9 oz. per sq. ft. or .185 oz. per sq. ft. respectfully.
Painting hot dipped or electro-galvanized materials is challenging because a layer of zinc is applied and the zinc makes paint adhesion subject to peeling and delaminating, yes - you could etch it with white vinegar or buy a special primer but you're dealing with edges and holes that are more likely to expose the cold rolled steel substrate.
I would use the G185, you're putting a lot of work into your project - I would also be mindful of the type of fasteners you choose for the hardware for the same reasons mentioned above.

Good Luck

Use the Right stuff

Eagleye has it right when it comes to the galvanic corrosion aspect of the treated wood and metal when they touch. Use the proper hardware and save the long term headache down the road!

Chris