I stick with pressures recommended by Giant/RS. I also found tire pressure as important as setting the shocks right. I was running tires with too much pressure but with lower pressure it revealed true nature and improved a lot. Now it feels perfect.
I have my fork at 100# and my shock at 200# and my tires at 36#. I weight 225 before gear, and these numbers work well for me. I could probably run 90# in the front to get more of the 100mm of travel used..but its real close.
FWIW, 2012 model, X29er 1 - I'm 260lbs and I run 100PSI on the fork, rebound a shade higher than middle, and the shock at 220PSI and I never use the propedal. Tires are the stock RRs and I'm running 32PSI up front and 36PSI out back.