well that depends on what you want to use them for. Terra do 3 setups. light/med/HD.
med is 200-300kg additional load
HD is 300+
not sure on the light.
you need to work out the weight of additional equipment you have added and propose to add. Ive gone med as i plan to add a cage in the next few weeks (100kg) along with my winch and other bits. most of the time the load area is empty so mediums suit my everyday requirements. When i go to Morocco, i will swap the rear springs for HD's to put up with the load in the rear.
G