Well, I just had the front and rear suspension stripped and rebuilt wit hall new seals, oils, regased etc and its transformed the bike, admittedly the suspension was totaly shot both ends before.
The guy who did it has been doing nothing but this for over 30 years so knows a little about it, and he said he now only uses rock oil as it doesn't break up, foam or go off as quick as other oils.
I am a big fat heavy bastard at 17 stone and find 4.5 rings showing on the front forks about right, rear shock has had the spring preload wound up a bit and the damping wound down a bit, can't give you exact settings, it has been trial and error.
From previous experience on other bikes, I know that fork oil goes off after 4-5 years/30,000 miles and the rear shock after about 25,000 miles, it can be a gradual thing that you only really notice after you've replaced oil/shock/gas etc.