Another quick question... RT's calculator recommends a .87 spring (142lbs). Obviously .85 is closer than .90, but I often ride 2-up and I'm more likely to gain weight than lose any so I thought I should go for the .90. Is that sound logic?
A 0.875 is derived by using one 0.85 and one 0.90.
This is a very common practice and A OK to do.
At least some suppliers, chassis tuners in particular, will sell you such a pair, and not force you to buy two pairs and be stuck with 2 springs.
I suggest no less than 0.875 and no more than 0.90.
No more than 15 mm of installed preload, no less than 10.
Remember that Installed Preload is determined with the Preload Adjusters fully backed out so that all the indicator rings are showing topside.
Suggest you begin with 10 mm of Installed Preload then set your Preload Adjusters inwards by 2 indicator rings, regardless of which spring rate you decide upon, then go from there based on road rides.
Suggest you use no higher than 140 mm of oil level instead of the stock setting.
Keep in mind that your 05 was a terribly weak rear spring in comparison to the pre 04s.
Keep in mind that 919 forks are harsh on bump, with that harshness manifesting itself like a stiffer spring.
Make sure there is some grease between the lips of the actual hydraulic seal that is below the dust seal.
If you ride two up, your issue will not the front springs, it will be the rear spring, and you'll have to dial in lots of preload by the adjustment collar.