0.010" may be a bit tight for a 0.011" B string, especially if the string is slightly over-sized. Saying that, I use a 0.016" file for my 0.017" G string without issues, so it may work. With the wider slots, you can normally get a folded piece of P400 or P600 in there to tidy things up and widen the slot if necessary, but you'd be hard-pressed to get anything coarser than a folded over piece of P2000 in a 0.010" slot, which makes any widening quite hard work. You don't want the string sticking in the slot because it's too narrow, as that will give tuning problems.
If you always use 9-42s, then I'd go for this set of 6 Hosco files, which are £10 cheaper than your 5 files.
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