IMHO, its not worth the extra $$.
I just recently put together a system and got the 2.8E processor (800mhz, 1mb L2). Its blazing fast. The 3.0E was like $20 more, but I knew it was'nt worth it.
One reccomendation is to get a tube of Arctic silver 5 thermal paste. Scrap off the compound that comes with the processor, and use some acetone on a q-tip to wipe off the residue. When you apply the new thermal paste don't squeeze the whole tube on the cpu, it will be way too much, and squish out the sides
There is cheap place to buy the arctic silver 5, use www.pricewatch.com
to find it. I paid about $7 inc. ship..