I've got to cut one hole for a shower waste (40mm - solvent weld
probably) through a cavity wall. I don't expect to ever drill one
again.

Is a cheap TCT core drill up to the job, I have a nice Makita 2Kg SDS+
to drive it? Or is it worth hiring a diamond core drill? I am 30
country miles from the nearest Hire Shop. The smallest seems to be
52mm though - and £44 a day.

I was thinking of this:

http://www.screwfix.com/prods/58613/...Drill-Bit-40mm

Not having done this before, should I really go for a larger, say 45mm
drill to allow some room to get the pipe through?

I know I'll also need an arbour and pilot, is it worth getting a short
arbour (100mm) to start, and a longer one (300mm) to finish?

And finally, how long will it take to drill?

Thanks,
R.