Rear Shock Lapierre X Control 310 advice needed

Hi, i have recently taken a 2010 X Control 310, the rear shock is set correctly as per guide but the rebound adjuster doesn't seem to effect the pace of rebound by very much, and the shock seems a little solid all of the time, any ideas or reviews on this rear shock and also a possible replacement??
The stock shock is sh1t, replace with Fox Rp23 (or the modern equivalent) they go for about €150 refurbished, James should have some in OC Tuning.