It's very good, but its not quite good enough

I'm having one of those weeks. I've been slaving away trying to get a large European Research Council grant application completed. It's taken me an absolute age to put the thing together as it really needs to be spot on given the chances of being awarded it are 2-5 percent. I had some feedback on the preliminary draft this morning. The verdict, 'it's very good, but its not quite good enough'. Rather than a bit of tweaking, the proffered solution (and unfortunately I agree with the assessment), is a fundamental rewrite and restructing. I've spent all day at it. I suspect it is becoming poorer with each draft. I had this problem with a story once. In striving for perfection it just got worse and worse and ended up in the bin. I'd have been better off leaving it alone. I'd be happy with very good, but its not the top 2-5%, is it? So, once again, it's back to a clean sheet.

Does anybody have any top tips for dealing with this kind of issue? All advice gratefully received ...