Thanks guys.
The reason why I use self cutting screws and timber fix bolts is so I don't have to drill a pilot hole
In any case, for the last incident I couldn't have got the drill in the space. I freely acknowledge that part of the issue is that the wood is pretty hard. Most of it was cut after the big storm in the 80s and has been in our barn since then gradually maturing, like me.
Oddly enough, I have very little problem with Pozi screw heads. I find that with good quality bits in the driver they don't cam out and can be driven in and out a few times as needed. I do buy proper impact bits.
Most of the screwing (so to speak) I have been doing lately has been fixing oak battens all around the inside edges of oak timber framing, to secure insulation in place, and provide a backing for cement board prior to it being rendered. I must have driven in 300 or 400 pozi screws and that is why I use self cutters. These battens will never be seen again.
For this building I bought a job lot of Reisser screws quite cheaply and find these drive in and out pretty well. 95% of the time the screw is driven in by the impact gun and will never be touched again.