when i was looking at cams for a GT turbo, i was looking at either straight 272s or straight 280s, both HKS.
i talked to one of the reputable evo tuners in socal asking what he thought about the 280s vs the 272s. he said that you might see a slightly higher peak hp with the 280s, but there is no "wow" that you need to have the 280s over the 272s.
maybe if you have a fully built head revving to 9k you might see a benefit with 280s over 272s, but at that point, why play around with silly HKS cams, get something with a higher lift that will take advantage of the fully built head.
of course looking back at this thread it seems to have gone from what cams to what turbo. if you want to know what i think. stick with a stock evo. get some R comp tires and a rear swaybar and bushings and stick with your autox. reading the thread, i can immediately tell you dont know what it takes to do well in what you want. hell, sell the evo and get a miata, it'll run circles around the evo at autox if done properly. it'll save you a bunch of money too.