For 1/2 all that matters is a S/N so your class doesn't really matter. Since I'm assuming doing a 1/2 in year10 means doing a 3/4 in year 11, the following information is regarding 3/4.
The people in your cohort is (supposed) to not affect your mark. It sometimes does when, for example, some people try hard at the SACs and give up on the exam but the strength of your cohort shouldn't affect your mark at all!
How it works is:
-Do SACs at school. The students are each given a "rank" within their class/es. (mark isn't used, only for verification. It's the rank that matters)
-Do exam at the end of the year. The students are again given a mark and a "rank" within their classes for this exam.
-The SAC marks are shifted to meet the exam marks. 1st in the class gets the highest exam mark, middle person gets the middle mark, etc. They try to make it as fair as possible. More information can be found here
http://www.vcaa.vic.edu.au/Pages/vce/exams/statisticalmoderation/statmod.aspxSo, in short, having smart people will mean the exam marks in those classes will be higher, and therefore the SAC marks will probably scale up more, BUT your rank will be lower in the class, so it cancels out. The people in your class shouldn't matter, you should get the same marks either way (but sometimes small classes or certain scenarios can distort the marks a bit)