I just got my first mac. Its the new base 21.5" iMac. I installed steam, then bought Portal. When it first loaded it defaulted to a number of things. I changed them all to the upper levels of performance, where it initially had lower levels. It also had a lower resolution than native. At first it seemed choppy until i turned on vsync. It then ran very smoothly. 1. Why did it defualt to lower settings if it runs well on better settings? 2. why did vsync on help?