I've been using a Quatro twin fin for the last year and love it to bits.
I'm only a light weight at 70kg and i think the board is around 72lts.
I use 160cm fins whether im using my 5.3 or 4.1 and have no problems getting up wind at all.
Until you try a twin fin you will never fully appreciate how good it is to push into a bottom turn in front of a solid wave with the confidence that it will hold its line no matter how hard you push
They will take some getting used to and you will have to adjust your sailing style
the first few bottom turns sent me straight over the front.
Try a few different ones as some are defiantly better than others and its not always the board that sails the easiest straight away is necessarily the best one,as i say they do take some getting use to
Get the wrong board and you could hate them and be stuck on a single fin for ever

Read the reviews and try to make some of your judgments from them
There is a new quatro onshore twin fin coming out next month that should be faster and early planing which i think will suit alot of WA conditions.
I will be queuing up to have a go for sure
hope this helps