Another Tire Question - 11 silly centimeters

[husker boxster]

My sister in Dallas has asked me for suggestions on tires for her car - a 2006 350Z Enthusiast model. It's her only car and obviously her daily driver, she drives fast (who doesn't in Dallas?) but not crazy fast. No track or DE days. Because Dallas gets the occasional ice or snow storm, I think she could use a set of all season tires. The tires that get very good reviews on TireRack are the BFG GForce Super Sport A/S and Yohohama Advan S4.

Here's the problem: front tires are 225/45/18. Neither of the 2 brands sell that size. I called TireRack to ask them what an equivalent size to 225/45 would be. He said you should never change the tire size on the 350Z. Not satisfied with his response, I visited my local tire store this afternoon and asked the same question. He totally side stepped the question and showed me a list of manufacturers that made tires in her sizes.

I searched for and found an old forum thread that explained how to decipher the first 2 numbers. With that in mind, I've done my own homework and here are my options:

225/40 - the width of the tire would be the same as the orig but the sidewall would be 11mm (7/16") shorter.

245/40 - the width would be 20mm (7/8") wider than the orig while the sidewall would be virtually the same (this tire would be 3mm shorter).

With all that as background, here's my question: Would you go with a slightly shorter sidewall, a slightly wider tread, or go with a different brand that has the exact size?

Thanks in advance.