The "ideal rib" with the "ideal engines" would cost around £150K..
..so lets get real.
Your £10k will get you the boat you're looking for. 100hp will do fine on the back of a 6mtr boat...... probably top around 40mph and cruise 25-30mph without any bother. My 6.5mtr does 43mph (4 up) with 130hp. tows two skiers and has covered the best part of 1000 mls coastal and offshore this year. HOWEVER....Fuel bills, two years dry stack, servicing ???
My fuel bill for this year will be over £1000. I trailer and keep at home but I'm guessing dry-stack will be £1000+ per year. I do my own servicing/maintenance and that will have cost me best part of £1000 this year. It's been a bad year! (includes trailer maintenance).
Generalisations always invite controversy and varying opinions but if you give a couple of examples of what you're considering buying, chances are someone here will have something the same or very similar and give you the benefit of their experiences.