Reducing Max no. of Retransmission will reduce SDCCH Holding time for sure.If your site is having a very high SDCCH Blocking ,reducing it will definitely improve your SDCCH Blocking.
Rach Success ratio=immediate asssignment commands/RACH requests.
Poor RACH suceess may be due to poor radio environment,like CO-BCCH-BSIC in nearby sites,Phantom RACH(especially in very low traffic sites),BTS sensitivity,No SDCCH.you can also increase the RACH min. access level(def. -105) to improve RSR.