Doesn't seem to be much of an issue getting over Stansted so long as you are confident on the radio and actually do fly at the height, direction and speed you say.
Be ready to take an orbit for seperation with their commercial traffic, be ready to expedite if you have speed in hand.
I flew Southend to Manchester (Ashcroft), straight over Stansted on the way out and the way back last weekend with no issues at all, likewise the week earlier flew to Wales and back from Andrewsfield, didn't bother to even ask for a crossing on the way out as you could hear that they were completely buried, but on the way back it seemed a bit quieter, we asked and crossed with no issues.
Bottom line, if it's been 5 minutes and so busy you can't even get a call in, don't bother, but other than that, ask away, you might be surprised.