Turns out cut was more like 29-30mm. Tried the over the bench method on a scrap piece but just ripped chunks out and took wasn't breaking straight despite a deepens score. These tiles just don't want to play.
Resorted to the new wheel on the wet saw as not confident of cutting straight with a grinder. Plus wet will hopefully last longer. Wow... Ok verrrrry slow but the cut is smoother than the uncut side.. And once tickled with the
Rubi block you have hard time telling which side it was.
Two tiles cut, brew then few more to go
Using one of the Abracs Expert diamond blades toolstation are doing for 9.99 just now. Only 115mm but fits the saw and grinder. Thin at 1.2mm but cuts clean with no chipping so far. Even if it only lasts this job out I'd be happy.