Hi y'all

looking at getting an xt660x and i've been searching the forums trying to find the answers but not to good on the ole search thing. I love the look of them and the sound, a bloke a my local sometimes parks up outside and not sure what cans he has but dam they sound good. Currently have a cbr600 fs-1 and a cb500 that i'm going to part chop.

I am looking for a bike mainly used for commuting in all weathers throughout the year and some weeks can cover 400miles+. Need something long lasting and practical but fun and I can tweek with myself n want that grin factor.

My questions are
I know about the surging and the modifications. So with a kevs air mod and filter say stage 1 will I need to adjust as the weather gets colder?

Will it improve fuel economy on the right setting? Can it shorten the life of the engine?

From what I can see depending how I ride I can expect anything from low 40mpg to around 60mpg, that sound about right?

Thanks for the help and have to say a great site where i've found lots of useful information and apologies if ive plaed this question in the wrong forum.

Regards