What is the poeples preference to bar sizes, I have been switching between a 45 and a 55 on an 11m and I am in two minds, I prefer the 45 bar as it just feels right but that is only because I used to fly smaller kites and that is what I am used to........! Sure it will turn a bit slower as you have less leverage but the smaller bar you can also whip it around.......?
Have you gone bigger and never looked back.....? 
I like small bars. Kite tends to be more stable and doesn't loop when you least want it to.
Unhooking on a short bar makes it better also.
Posting that here is like asking what is the best kite to use. Try doing this, ride with the bar your most comfortable with and thats that. Theres no science in it. Just do what YOU like and all will be good.
Ok. Lets use an Air rush Vapour X for example. I borrowed one from a friend as the wind was a bit strong for my 12m. The kite is a 10m and i found it to be a little slow for me, but after i extended the bar out to it's maximum i had a ball on it. The owner always uses it at it's shortest setting as it suits his riding style. The bar can be adjusted to suit the riders preference. If you like a shorter bar to slow the kite down for more stability and slower turning, thats ok. but i prefer my kite to turn fast and that dosent suit all riders. It comes down to what you like, not what your told on here.
I agree with Jas, I use my 8m bar for the 11m all the time. I prefer the smaller bar because I like my kite less responsive so when I'm upside down doing dangly spinny tricks I don't have to worry about which way the kite is going. To answer your question I dont think it works both ways. In my experience when I use the big bar on the small kite, the kite just doesn't work like it should. It just overkills the turning... I guess that's why they make different size bars for different size kites...
