The E6400 is the faster processor than the A64 X2 4600+ at stock speeds.
For the record, overclocking is safer than ever before. The chances of you frying a component in your system are minuscule if you do it right (and doing it right isn't that hard). Chances are that even on a heavily-overclocked CPU, you will never (ever) need the warranty. The PC will be sitting in a garage a decade from now before an overclocked CPU runs out of it's lifespan.
I relate to something like buying a processor that runs at 3.2Ghz and choosing to run it at 2,13Ghz. =/ A major waste of money, in my opinion. The E6400 would easily overclock to over 3Ghz and leave any other processor out there in the dust. No Athlon 64 processor would even come close to touching it.
Check out these benchmarks.
And those are processors overclocked to a pathetic 2.60 and 2.88Ghz. They're capable of much more.