ok, not sure what you have done already to your tC. but unless you are going with some wild aftermarket cams, you don't really need all that done. also, unless you are FI or completely Built NA with some high compression, you don't really need that done. i would say on a bone stock motor, 2-5 hp increase. you'll notice it in the top end, it may even hurt your performance on a stock motor. with FI you might see 10hp but i doubt it. it'll help you hit boost quicker tho and let you flow more cfm's.
hope that helps you.
hope that helps you.