HDD 16mb cache vs 32mb cache

[Matt Rushmore]

I've looked through a bunch of threads on here and while I have found a couple that say 32mb drives give better recording performance, I can't find any that say how much or how necessary it is.

Why I ask:
I have two 500gb Caviar Blue 16mb cache 6.0 gb/s drives (one system, one recording). I am going to buy a third drive for samples. The easiest drive for me to get locally is another Blue (3.0gb/s) with a 16mb cache.

But, after reading the duc and the web I am curious if I should go through the trouble of ordering a 32mb cache drive (either a blue or black) and make that my recording drive.

Which poses another question since my motherboard only has two 6gb/s sata ports, could I put a 6gb/s drive on a sataII port? Or would it cause issues? Thats what I'd kinda have to do if my new drive was to be my new recording drive.

OR, maybe get a 3.0 gb/s Caviar Black 32mb cache recording drive? And leave my 16mb drive on my 6.0gb/s port even if its used for samples?

The choices make my head spin. haha

Thanks for any opinions.