I wasn't aware that the Cobra MkIV did anything well.
Apart form losing out about 1.5ly to the Cobra III in explorer get up the MK IV outshines it in almost every way.
The only thing the MK III has over the MK IV is speed and ship kits (not mentioning a really over zealous fanbase) after you get over the speed issue the MKIV can do everything better than the MK III apart form racing, see speed comments.