I'm a little confused by the replies to Niels question regarding trim tabs. Surely, if my understanding of the purpose of tabs is correct, they can only enhance the charecteristics of his hull.
To say that they won't work on a sub 7 metre boat is incorrect. Why do you think they wouldn't work?
Infact, take a look at www.bennettrimtabs.com
, they have sizing guidlines for boats from 15' upwards.
As for powerlifts, I can recommend both Stainless Marine and Bobs Machine shop. Both excellent products, although I prefer the Stainless Marine version.