Here we go again......
This very subject has been debated on the forum ad infinitum in recent months without, it must be said, a definitive answer.
You don't mention whether 2 or 4-stroke. 4m Searider transom is rated to 110kgs and maximum of 50hp, although Dave Manning has owned 4m Seariders with a 70hp, but when you live in Wolverhampton, hey you need as much excitement as you can get. He'd be the one to talk to, or Rogue Wave, another Searider afficionado.
I understand the main issue with too much power on the 4m is the risk of chine-walking, although again there are those on the forum who'll tell you this isn't necessarily a problem. However, Steve at Fineway Leisure in Norfolk, an Avon premier dealer who sells shedloads of Seariders and is well respected, reckons the Mariner 40hp EFi is the ideal engine for the 4m boat and that even the 50hp is a bit over the top.
By the way the Mariner 2 stroke 60hp weighs around 100kgs and 4-stroke 60hp EFi weighs 112kgs. Let the debate begin..........