If it was mine, I would cut it and chop it for silage. If you have a good relationship with your neighbor, he will probably give you just as much as it would as it would bring for hay. You can figure it out by Dry Matter-hay would be 15%(85% DM) moisture or so, and silage would ideally be 65% moisture(35% DM).

4T hay x .85=3.4 T DM. Then, 3.4T DM/.35=9.7 T of silage.

By making silage, you sidestep most of the weather risk, and your neighbor gets better feed. It also gets the material off your ground a few days sooner and would allow you to plant whatever that much sooner.

If you left it for combining, you would have to deal with the ryegrass in the combine, and have poorer straw(if you sell that).

If the seed heads are out, prime time for cutting for dairy feed was a couple days ago. You would need to act fast if you go that route.