For me I'd have said too much, unless you were planning on a mid-July or later BG. I binned my first BG attempt at Wasdale and certainly wasn't recovered fully 5 weeks later for my 2nd go.
It's a very individual thing though, and if I'd have done the Fellsman I know I'd have given it everything and just wouldn't have been able to treat it as a training run even though I'd know there was a bigger goal in mind. It's proven successful for a lot of people though. My preference would be the OCT if you wanted a fairly long event in the build up.