Greetings from the UK.
I also take 5,000 iu’s daily since I agree that, since we live in the UK and I work indoors, we are likely all deficient in it. And I love it. That and ZMA are the only supplements I take year round, without fail.
I have been taking it at this level for maybe 7 years now and feel the better for it. I rarely get ill (last week is the first time in 7 years actually, a record I was sad to say bye to) and like to attribute my immune strength to not being d3 deficient.
Saying that I have found very different qualities, and in particular if the d3 isn’t oil suspended (so comes as a hard chalky tablet rather than a gel cap) I don’t feel the same benefit and there are those that suggest it is less bio-available in the non gel form. Cheaper isn’t always better with supplements.