April 23rd is as good as any and better than most except for the rare occasions when it coincides with Easter.

One thing you shouldn't do is take any event after 1603 and describe it as English, because after that date the concept of the UK came into being. That's why Trafalgar (1805) wouldn't work. Comemmorating battles will always end up offending someone. Best go with a semi-mythical middle-eastern good man or a dragonslayer, I reckon.

And I'm still up for a Shakespeare Supper, as long as it wouldn't feature the main dish from Coriolanus or Shylock's delicacy.