071's area good plug that suits most tunes, but for stage 1 you could use AGPR12PP8, these are precious metal ones, so about £40, but with a group a coil work wonders.
You can get these bits from Matt Lewis 01922 692424, and you WILL notice a smoother idle and better low down with the plugs/coil.
It could be blowing the spark out but does NOT cause cut outs normally, just a wall of no extra boost, just revs as does not create enough exhaust gas to spin turbo very fast, as intermittantly misfiring, all you will feel is no power, no real roughness.
Use a 0.65mm gap as this works well, also make sure you have decent leads, like Magnecor etc.
tabetha