setting max resolution doesn't make small. I am serious. I always set max it out because it looks right. but I doubt if you set max resolution for MBA, it will show 40fps? I doubt. 9400 graphic card is not dedicated. it's replacement for intel shared graphic chip. so intel customized for only apple. so that's why it performs sucks.
I don't play games on mac because performance issue even I have two. especially, when you play on this MBA, it is most likely suffered test how MBA is getting suffer. I am not sure whether assassin's creed 2 for mac is released. but if it is released, you'd better test real performance. bioshock is required very low system spec.
oh, I found that actually mac version of assassin's creed 2 is available now. so you should try. here is a link.
http://www.macgamestore.com/product/1612/Assassins-Creed-2-Deluxe-Edition/
System Requirement
Minimum:
Mac OS X 10.5 / Mac OS X 10.6
PROCESSOR: Intel Core 2 Duo 3.06 GHz
RAM: 3 GB
VIDEO CARD: 256 MB Dedicated Shader model 3.0 or higher (ATI RADEON HD 4000/5000 series,
NVIDIA GeForce® 100/200 series)
HD: 9 GB
PERIPHERALS SUPPORTED: Keyboard, mouse.
INTERNET CONNECTION: Broadband Internet connection with 128 kbps upstream or faster
Recommended:
PROCESSOR: Core i5 2.66Ghz or better
RAM: 4 GB or better
VIDEO CARD: 512 MB Dedicated - ATI Radeon HD 4850 , NVIDIA GeForce GT120 or better
Laptop and integrated versions of these cards may work but are NOT supported. These chipsets are the only ones that will run this game.
I don't think that 13 inch MBA will run this game. why just don't people admit MBA is not for gaming? come on. if you disappoint performance, get over it. it is for mostly simply works.