Girvin I've tried my 856 with Bombers, works ok but for me all my Flex's have Girvins. Not sure PACE would suit, they are better fitted to Oranges, both my C16R's have PACE and so will my Clockwork shortly
It's your choice, what are your main priorities? amount of travel? weight? looks/colour match to rest of bike?
In my opinion the Girvin/proflex combination is an iconic image of he 90's, they just look so good together. But other forks can look good on a 'flex and save you some weight too, I recently swapped my Crosslink forks for Pace RC38's on my 857 and apart from the weight reduction I find the air forks much plusher, and the carbon on the forks matches nicely with the carbon swingarm on the frame
I would try the Bombers on there and see what they feel like, if you're not happy then stick the Vectors back on. I'd probably give the RC35's a miss.
As above really. Girvins if you want to stick with the classic Proflex/Girvin combo or Bombers if you want better performance.
Pace if you have an Orange.