I’ve said it many times before and I’ll say it again.
If you need to get rid of lots of varroa in the middle of winter (over 500 mites reported by beano?) you have missed the boat.
A great number of your winter bees will already have been infected, with viruses, by the varroa nymphs feeding from them while pupating. The best time to rid your colonies of varroa is just before the winter bees are produced, thus encouraging a cohort of healthy bees to take the colony through the winter and into the spring expansion phase.
One only needs to look at the carpet of dead bees (or lack of it) on the hive floor, in the early spring, to understand how important it is for healthy bees to take the opportunity to increase the worker numbers in the all important spring expansion phase. Dead bees are utterly useless for that!