Now that I have dismantled my crank a few questions (perhaps stupid ones but, what the heck!) have come to mind.
(1) When the spline/spindle is inserted through the bearings what stops it doing the turning and the bearings staying still? Is it down to the tight tolerance that sort of 'wedges' it into the bearing to ensure that the bearing is doing the work? Would the application of some loctite ensure the right part is always doing the turning?
(2) Could the mating surface on the spline/spindle ever become worn to the point where there would be minimal contact with the bearing?
I'm sorry but, I was the kid who asked lots of questions in school
IF i'm thinking this correctly, when you push the spindle through the bearings and tighten the opposing crank-arm down,- It "pulls" the crank arms together, (like the headset) and Thus squishes them against the bearings (like you thought)
Anddd No, the mating surface on the spindle can't become worn because it doesn't move
against something, it moves
with something - the thing that moves against something is always the bearing against the race, which subsquently is the wearing part.
- Also, like you'd probably imagine, if you overtighten the 'squishing' force you will get less smooth bearing rolling and increased wear. So make sure you tighten your cranks up properly, which is typically fairly snug with a good size allen key but nothing to get a cheater bar out for
No question is stupid if you feel the need to ask it
-- Edit, In reply to your main question however, I recently serviced my PF30 bearings without taking them out of the frame, I used this lithium grease, yellow looking stuff, very thick but ive used it for all sorts.
I recall asking an old guru at my bike shop whom i worked with if the stuff was any good and his answer was "It covers just about anything"
So since then i've just used that stuff. Ages well, doesn't like water though, but works for Yonks when you keep it dry, good bottom brackets like yours and mine have decent seals anyway, so I tend to not care about weather resistance.
It doesn't matter how thick your grease is, if you pack it well and tighten it down, the excess will squish away and you're left with all you need.
Just don't fall into the trap of using "bike specific grease" which is priced stupidly high - i've used stuff advertised for industrial and car related bearings, which you can buy in bulk and do the same job in the same circumstances.
Remember, bicycles are a vehicle not a vintage clock. We don't need any specific products.
Keep in mind what I said about tightening too hard though, that can cause you to be changing grease and bearings too much too. (Fresh grease always causes noise especially when packed hard.)
