You have to love Mac Rumors.
How many people on this thread actually own the 3.33? I am betting none.
I believe the OP was asking if he would see a difference between the 3.06 and the 3.33.
To answer the original question, yes you will see a noticeable difference in performance. Not huge but noticeable. On average 10 to 15 percent or higher. That is considerable And once memory gets cheaper you can upgrade to the 1333Mhz Ram instead of the 1066 Ram. The E8600 3.33 supports the faster Ram. As opposed to the 1066 in the 3.06 C2D.
I don't see how a 27 screen has anything to do with performance.
Some people don't actually want a screen that big. Regardless of price. And yes the 27 is worth more due to the screen and will sell for more regardless of what processor you have in the 21.5.
I have owned the 21.5 mid level version and traded it in for the base with the 3.33 and noticed a difference in performance right away. And comparable to the low end dual Core i3 and i5 in performance in some tests. Overall the Clarksdale's are true beasts, much better than any Core 2 duo. I would wait and buy a imac at the next refresh. If you can. March is not far away or if sooner. Apple is announcing a new imac touch supposedly on the 27th of this month. And maybe they will announce something else. Doesn't hurt to wait.
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=3704&p=7
http://www.cpubenchmark.net/cpu_lookup.php?cpu=Intel+Core+i3+M+330+@+2.13GHz
http://techreport.com/articles.x/18216/10