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Shorter the runners, the more you will gain top end (if the engine can breath correctly up there), but will be giving up power in the low to mid range instead.
Hence with fast intake, it not just the few HP you gain top end, but the 10HP that you will gain in the meat of the power range with the long runners instead on a LS2 type engine. On a LS3, the stock intake is very good (they solve the sonic welding problems of the LS2 intake), so really not gaining much with the fast intake instead (not the price for the few HP you gaining at over $1K when its all said and done)