18s help picking tires

[Eighties Meta]

ok I need some help after searching the forums still pretty damn confused about what I can do:

the car:

2009 370z Automatic
Touring (no sport package)

stock tires are:

Front 225/50/18
Rear 245/45/18

I'd like a wider tire in the rear but I want to remain on the 18 inch rims and I'm also going to go with ALL SEASON tires year round as I think the Dry grip should be just fine.

according to TireRack.com an optional size for the rear is 275/40/18 on my car but it doesn't list an optional size for the front. so my question is do I have to run 225/50/18 and 275/40/18 in the rear?

or

Could I run 245/45/18 in the front and 275/40/18 in the rear. The Tires I'm looking at are the :

Michelin - Pilot Sport A/S Plus
Front 245/45/18

and

Michelin - Pilot Sport A/S Plus
Rear 275/40/18

could anyone offer some input as to whether this would acceptable for my goal of a bit wider tire on the rear, adding an all season tire since I will have to drive this in bad weather on occasional and hopefully the tire will perform well in dry weather. The car won't be tracked and I plan on doing the tires after I get my car back from AAM Competition because they'll have it a few days for some performance mods.

Thanks and I appreciate any advice.

Eighties Metal
Kevin