E6300 is just about the worst C2D to select from an overclocking standpoint, since it requires an expensive mobo and memory to handle the high FSBs needed. OTOH I got an E4300 when it first came out and have been running it at 100% overclock (3.6GHz) ever since using inexpensive memory (1:1@800MHz so not even overclocked) and a relatively cheap board for my game machine.
No, in normal use it doesn't feel
any faster than a good 3+GHz Northwood setup (because the bottleneck there is generally the hardddisk) but it is
way faster in games (note that most games are limited by the video card but simulators like flight sims are usually cpu-limited). Quad-core and large caches
still do not provide any significant gains for such uses compared to extremely high-clocked dual-cores, so unless you are looking for bragging rights it is far better to drop the extra money into the video card for gaming (have an 8800GTX)...
For
work, all of the workstations I have here are running seriously undervolted (1.25v) Northwoods because they are quite fast enough at default speed, and any more results in far more noticeable heat output than performance improvement. Overclocking in general is also probably not a great idea for a work computer, and you wouldn't be doing anyone any favors by
folding with an unstable machine either. How would you feel if that elusive cancer cure was delayed because of errors from your machine?
Super Pi and Prime95 are excellent stability tests but my experience is that a machine that can easily pass one test for 24h can fail another immediately. Couple that with the inevitable degradation over time (dust buildup, electromigration from scary high voltages) and it's probably best to only run a machine on the ragged edge if it's for "play."
Remember folks, compared to a machine from a dozen years ago,
The CPU can now be 200x faster in terms of MIPS
The memory can be 30x faster than the old asynchronous simms
The hard disk sequential transfer rate can be 10x faster
The hard disk average random access time is...
exactly the same or even worse
What do you think is the bottleneck? Given that, do you really think a faster CPU can
ever really feel like "all that" much of an improvement for general web surfing use?

I mean, check out a slow CPU with a
really fast disk.