Judering under hard acceleration

I know that I'm probably going over old ground here but my 2004 Octy Mk 1 has developed what can only be described as a judder when accelerating hard in 2nd & 3rd gears; once the turbo spools up and it gets up to about 3000rpm the juddering kicks in.

It doesn't appear to affect the acceleration (not that I have noticed anyway), but when it starts I obviously lift off; on the couple of occasions when i keep my foot in it seems to clear itself.

I changed all four coil packs about eight months ago and had to change the coil pack on cyl 1 last week; I had also bought a spare coil pack and fitted this to cyl 3 (not sure if that was the right thing to do now??!! ) juddering didn't go away, so had a play around with cyl 4 and still no difference.

Now is it going to be running down the usual check list of sesnors, TB, MAF etc? I don't really want to purchase another two coil packs for no good reason if it turns out to be something else??

One thing to note is that I have been running it on super unleaded for ages but when I lent it to my OH last week she filled it up with 95RON instead , could this have had anything to do with it?? Could this have put stress on the ignition system and cause the coil pack to fail and another to become faulty??

Any help or advice appraeciated........Thanks!!