I have a friend looking to buy an older 28-30 skater and putting new power on it. What is the most effective & efficient out there on the east cost?

Most of the 28's I know of have already been repowered. THese boats are like gold, don't even dream of finding a "steal".

T2x

Most effective and efficent would have to be twin 300x motors. One problem, they dont make them anymore. If you can get your hands on a couple low hours 300x, that would be the best bet. The 2.5 boats are fast, quick and handle probably better than any 3.0 setup. However, since you are buying a used motor, you have the option of running some custom 15" midsections which will be the closest weight setup to a 2.5 boat. The 300x's will be far more reliable and probably faster on the top end, although its close. Great running boat once you learn how to drive it.

If you are going to get new power, you should look at the 300 xs. They are much more fuel efficient than the 300x, although they may be a few MPH's slower. Even the 250xs isn't a bad option. I test drove one last year and it ran 96 MPH and probably had a little left in it with the 250's.