22 inch tyre help!!!

[Trickyd1609]

Hi there guys im really struggling with some wheels ive bought...maybe ive got my fingers burnt but we live and learn hey, hence why im on here so hopefully you guys can shed some light!

Ive bought a set of alloys for my X5 E70 with (9x22 front ET20/10.5x22 ET25 rear)

I understand that the offset is different to my current/stock 10j and 11j staggered 20 inch set up of ET35 and ET40 and these 22's will need spacers i.e 35mm rear and 40mm fronts.

Its the tyres im struggling with. The current tyres on there are:
315/30/r22 rear
285/30/r22 front

After using the overall diameter calculator i see that:
29.44 (747.8) 28.73 (729.8) -0.71 (-18) -2.4%

Is this workeable, i.e it wont cause any problems with my car? I did see somewhere that said the rears should be 335/25 r22 but the tyre prices for these are astronnomical and like rocking horse doo-da so im hoping this 315/30 set up works with the 285/30 on the fronts?