Just for comparison, I have the medium weight range OME springs on my vehicle, the front to cope with winch and bumper, the rear to cope with a rack and tent with a replacement rear bumper, if I start hanging spare wheel carriers then I may need to upgrade the rear springs again, before I mounted the rear bumper the rear axle would occasionally skip off bumps but the ride was not jarring or uncomfortable and having driven a variety of modified vehicles it did not trouble me.
Also the cornering was better with less body roll due to stiffer springs on the front, This was initially of some concern to me because I feared it would negatively influence axle articulation off road but so far there has been no problem. Before the change to OME springs my passengers would frequently comment or become alarmed at the degree of body roll, much to my amusement as I was used to the vehicle and I am fairly spirited driver.
) 868's are the +600kg rear springs, with the 864's being +400kg and 863's +300kg (OME part numbers). I'm assuming you've under estimated how much weight you're carrying and that 'Iron Man Expedition Spec' is probably equivalent to OME 863's.
