d-series turbo will give you a good deal more HP then a stock b16, but you have no more room to grow, other then rebuilding with forged parts and adding a bigger turbo. If you go b16 you wont have the 250 your looking for, but when you add the turbo you'll have a lot more room to go with it and there is a wider arrary of performance parts availble for a b series. If you want to go cheap, consider a LS turbo. There pretty easy to obtain from a junkyard and boosted there pretty nice.