2835 pro s gets my vote
i make a lazy 251rwkw (337rwhp) with 11 flat afr...
but get the KIT, its so much easier with the kit its directbolt, also you DONT need a gasket for the turbo to dump pipe. i spent a few weeks tring to get incontact with hks etc to get the gasket and in the end hks reply with "the HKS GT2835 PRO S DOES NOT need a gasket at all"
ohh im not sure how the 3037 does with lag, but i dont really notice it that much with the 2835 i get full boost between 3000 and 3500rpm