I think maybe you have misinterpreted what Dr Davis was suggesting.
Getting up to 60ng/ml is generally fairly speedy if you use 10,000iu/daily BUT your levels may tend to plateau once you get around that level. If you then settle down and continue to take that same amount and your levels doesn't go up or down but sticks around that 60~70ng/ml range you may think you've got it sussed and don't need further tests.
What Dr D finds is that around the 3yr mark SOME of his patients find that their reserves are full up and rather than keep piling Vitamin D3 into store the cells don't accept any more and circulating plasma levels start rising above 100ng/ml.
As this point you can assume reserves are full and you can safely reduce daily intake so you return to around 60ng/ml.
It is only around 200ng/ml that toxic effects of D3 have been recorded so at just above half that amount there is absolutely no need to panic. It's just that there is no known benefit to having levels higher than 100ng/ml at the moment. (Although there is some reason to believe that above 100ng/ml vitamin D may have a DIRECT effect on killing cancer cells) There is also some reason to believe that keeping 25(OH)D both HIGH and STABLE is safer than having swings in status. When they've used ANNUAL vitamin D megadose supplementing it was counterproductive for some, and in Finland there have been suggestions that prostate cancer people who had the greatest range of 25(OH)D over the year had worse outcomes than prostate cancer guys who had even 25(OH)D levels through the year.

Vitamin D3 (like Melatonin) is an anti oxidant and one of the most important things anti oxidants do is to protect your mitochondria from oxidation. Dysfunctional mitochondria are the source of trouble in most chronic conditions so protecting them is the best way of staying healthy and delaying/slowing the ageing process. While of course it is a good thing to have sufficient circulating vitamin D3 to deal with problems it is is even more important to have anti oxidant protection built into every cell in your body.

This is why IMO it is better to raise status to around the 60ng/ml level where we know we can measure vitamin D3 in tissue rather than stick around the 40ng/ml mark where there is no measurable stored reserves of D3.