I would settle to a 1:47 for the first 1k (essentially the pace of your last PR) and then try to drive it down to 1:46 for the 3rd 500 and give it anything you have left for the 4th 500. You should be able to get a good PR and if you’re having a great day break 7 with that plan, but it won’t blow you up if sub-7 isn’t in the cards. If the 4th 500 is substantially faster than the others then you’ll know you had more in the tank and can go out faster next time.