@BewareOfDragons
Tell him he's a twat. You've always wanted a man with a six pack and a bigger penis, but you've kept silent all these years...
Say this, but don't say he is a twat. Don't drag yourself down to his level.
Just drop into conversation that you have never really enjoyed sex, because his penis is quite small. Act all concerned, (head tilted,) and say 'it's not your fault though hun (yeah say HUN, it's nice and patronising!
) And 'don't feel BAD about it hun.. lots of men have smaller than average penises...'
Apart from all that, I also feel rage reading your OP. What a thundercunt your husband is!
Sadly, you are not the first to have a husband or partner who is obsessive about his WOMAN staying slim. Sometimes I wonder if it's that they don't want their mates to see them with a 'bigger' woman. Men take the piss out of each other, and a man with what is deemed as a bigger woman/chubby/overweight will be mocked. (Although you sound fine anyway, and not overweight at ALL!) 
As has been said, he DOES sound like a horrible bully. I know a man who has always been obsessed with his women being thin, not slim or curvy or athletic, but THIN. Every one of them had to stay at a size 8 or less, or he would go cold on them, and tell them they had let him down, and no man is attracted to 'fat birds.' Vile twat. Your husband sounds the same!
But yeah @Bebub - play him at his own game!