I think if your rocking the larger 19" size the tyres don't make as much of a difference as they do with the 18's OEM size.
I have 452's on my 19's and RE050A's on the Rays....hands down the Falkens have more grip in the wet and dry. But is because they have a lot more rubber on the road than the bridgestones I imagine.
For 9k your going to be stretching to get a 313,...for 10k there are some nice examples around though.
As an FYI the 06+ is £480 a year to tax also. If you like one wack a link on here and we can help you out, Good luck
Just had mine done yesterday! Great bit of kit.
What will you be charging for the Z out of interest? I have paid between £54 and £72 for the Z in the past but always worth going to a specialist.
For the 6 spoke 18's the fronts are 8J and rears are 8.5J. ET30 and ET33 respectively.
So 265 is probably the largest rear width you would get on.
£300-£500 for just the Rays depending on condition. They do go for more than this but they will have OEM size tyres on.