Wanted to give some positive news on this whole 'not enough sensitivity / difficult or impossible to cum' thing.
Had a punt today - vanilla stuff, which is really all I'm into - but am pleased to report success. I managed to have a really awesome climax during penetrative sex, and in fairly standard missionary position. This is something I've struggled to achieve for a while, as anyone who has read my previous posts on this thread will know.
What's made the difference? In order of priority:
1. Wank ban - exactly one month has passed since I started this ban, and I think it has paid off.
2. Not worrying too much about the ending, but just enjoying the situation for what it is, whatever happens.
3. A generally healthy lifestyle, plus I take daily supplements of zinc and l-tyrosine. Obviously I cannot claim, let alone prove, that these have made a difference, but for the sake of completion, it's best that I mention them.
4. 25mg sildenafil an hour prior to punt. This is a low dose and taking it may be more psychological than physical, but worth it in my opinion. I did once try a higher dose but found this had a negative effect on sensitivity, the exact opposite of what I was trying to achieve.
So, anyway, I thought it would be encouraging to report some good results from all this, and hopefully it's onwards, upwards and better from here.