well, the point of a rush is to grab them before someone else does. equipping comes later
and while above 5K is optimal, a 4K province will return 80% of what a 5K province does. Actually, a bit higher than 80%, if you hunt like i do, w/ 3 priests w/ dousing rods, since that will, on average, drive the unrest up slightly.
so 4K is ok, while 6K (since it can Last a long time), is optimal. But, for instance, in my current game I have no 5-8K provinces, so my choice is between doing 4K provinces or 9K
