Tip of the moment. (not good enough for the whole day.

):
Render lighting tests in normal mode but REALY REALY small
Final res 2170x1470 to reach sample 17ish 67+ hours
Light test 217x147 to reach sample 17ish only 7 min!!!
The times above are from my memory about a week ago, so I could be a little off. Ill check my log files and send up some samples to show you what I mean.
Hope it helps, it saved days of test render time for me.
Dan