There are three processors there with 3.4GHz core speed.
The 3.4C has 512KB cache, the 3.4E (Prescott) has 1MB cache,
and the 3.4EE (Extreme Edition) has 2MB cache. You'll need to
visit a few review sites, to see which is faster and for
which applications. The 3.4EE is not available at retail
(I checked three sites) and will be about $1000 US or so.
The others will be less than half that.
To see what Intel is selling this month, check here.
These prices are wholesale for 1000 processors at a time,
so retail prices will be a bit more.
Biggest as in fastest? It would be undoubtedly the 3.4GHz Pentium 4 Extreme Edition (EE).
The 3.4C (Norwood core) is faster than the 3.4E (Prescott core).
In terms of over-clockability, the 2.4C or the 2.6C can over-clock much higher. With proper
cooling (phase-switching type), you can approach 4GHz with the 2.4C chip, but probably not
with this motherboard.
