Going with a charter is great - it's a proper holiday - chill out, relax, fish - let the skipper and crew do the hard work.
Going with a charter enables you to glean alot of info, esp. from someone like Rob - get a feel for the island and the fishing from a big fast, stable boat - leanr about the tides, races, dangerous areas, best times and tactics etc...
Going solo - is also superb - a real sense of adventure, a real challange - your on your toes for 4 days - you need to think all the time about the tides, weather, timings and tactics. It is VERY tiring - very... in fact I always book the day after we get back off work - I'm shattered!
So - both have merits it depnds on what you want out of it.
As CC says - the weather will probably make the call for you - but of course you need to make your gamble before the weather does!