I have only seen this done for real out of Bristol when fat for southern Spain or the Canaries. If you aren't familiar it's a hilltop airfield with terrain falling away and a very short runway. I have done SE flap 25 in the sim and the climb gradient isn't great at all, but we dont operate out of short runways in mountainous terrain so can't comment I'm afraid.
Our aircraft don't have the SFP mod either which may make some difference but I haven't got any experience there either.