The LT4 hot cam kit is a good deal, and there are a few people at this site that are running with it. I would think you would be close the 300 hp your wanting with this kit and maybe a couple of other improvements (programming out emissions, shorty headers, cold air intake, and possibly higher rated injectors).
Depending what your goals are with the turbo, you can probably get a cam that would work better with it. I would think that if you put out all the money for a turbo system, you would want your engine to be setup to make use of what it can do for you. I would figure out what you want your engine to be in the long run, and then purchase the items that will get you there. You can waste a lot of money buying things like a cam and then finding out you want a different one later.