Personally, I think the real answer is not going to be very popular. The Apex book is 300+ pages in the U.S. because it will have the cars and tracks. Where as in Europe it will only have 200+ pages because the coffee table book will have that info.
So, my assumption is that if you live in Europe and you want everything that will be in the U.S. edition... you will have to buy the Signature Edition.
The reason I think that is simple. It basically says it on the site.
From the UK Site:
Collector's Edition
200+ page Apex drivers magazine with hints on driving technique, car tuning, future technologies and more
Signature Edition
-As well as the game, the Apex drivers magazine and the ChromeLine car pack, youll get:
A Signature Edition coffee table book featuring the beautiful cars and locations of Gran Turismo
From the US Site:
Collector's Edition Content Details:
-In-depth 300-page car-lovers guide written by the experts at Polyphony Digital, covering everything from the history of the modern automobile to driving techniques and game reference material
Then again, the Collectors Edition in Europe is significantly less. So, it's not entirely unfair. But I guess thats easy for me to say.