Account registration form – newsletter opt in – during or after?

Will be implementing this as an A/B test soon, but I've been looking for any research or examples and haven't been able to find any.

We have a standard account registration form. It includes the usual newsletter signup checkbox (unchecked by default) as part of it.

I'm testing whether it's best to ask this question during the sign up or after?

My proposed change is to lose the newsletter question from the registration form (cuts down on up front questions.)

Then on an account activation, the user is presented with a welcome screen, which then provides the newsletter opt in question. The other benefit of this is that it covers for registrations from things like social providers and .

Just wondering what the thoughts are on this? Would be good to know if there is any data relating to where this question is asked.