So, I own the games both for Mac and PC, and both the original and the EE versions. I have no problems like this in the PC version. I also used to play BG1&2 on this same Mac, with no problems whatsoever.
I own a MacBook (13-inch, not Pro, late 2009). I use this machine mostly for work and during travels.
Processor 2,26 GHz Intel Core 2 Duo
Memory 4 GB 1067 MHz DDR3
Graphics NVIDIA GeForce 9400M 256 MB
Software OS X 10.9.4 (13E28)
BGEE and BGEE2 both start normally, without any issues. After a few minutes in game, things will start to lag a bit, and there is a perceptible slowdown.
There is a small lag between the moment I click with the mouse and the game reaction. This is the same for keyboard input.
The game becomes very slow, about half speed. Even if I reload the game (or quickly exit the current game and reload without closing BG in the process), things stay slow, and only when I close the game and reopens it, it will be normal again - for the next few minutes.
Is this a common problem? Is there any fix for it?