SDS Drill and Core-cutter bits

I want to use a core-cutter to drill a hole for my new boiler's flue. Two questions:

1. HSS charge 30 quid to hire a heavy duty drill SDS for one day. I see Screwfix are selling cheapo versions (quote 94802) for the same price. Will this do for a 107mm core-cutter bit? Obviously, I would rather buy than hire, given the price is the same. But not if the cheapo won't do the biz.

1. HSS only hire out 100mm or 125mm core-cutters. I want 107mm. Where do I best hire/buy that? Or will 100mm do for a 100mm flue. (Vaillant Ecomax

Thanks

Geoff