What's the realistic approach to this though? I don't know anything about this area, but to me it seems like hoping for 20 countries having 50 each would be effectively the same as hoping for 20 countries having 0 each.

That is to say, we're in the arms race because each country did have N each. But then one country had N+1, and so the others raced for N+2, and so on. If we hoped for 50 each, wouldn't it drop back to the same pattern, and someone would become 50+1?

Note that 4,000 of course doesn't solve the N+1 issue, but my point is if you're going to aim for 50 - I'm not sure what problems it solves. May as well shoot for 0, no? 0 seems equally impossible to me as 50, but at least it solves a single problem.. nukes, in general.