The thing with overclocking an eMac is that it's a pretty big deal.. you have to tear the computer down, remove the logic board, and desolder little teenie weenie jumpers, then put it all back together and see if it worked.
Processors are tested and rated at a certian speed they're shown to be reliable at, then usually sold as being slightly slower than that tested stable speed.. so in many cases, you can get several hundred more megahertz out of a chip than they stamped on the top. (I run a 700mhz eMac at 900mhz, for instance)
Now some guys are able to get them going 1Ghz or faster, other guys have problems when they clock a 700mhz chip to 800mhz.. there really isn't any way to tell how much faster you can push it until you tear it down and try it.
So before ripping into your computer, ask yourself if the possible speed gains are worth the effort.
At 1Ghz, i'd think a faster, cached drive and more RAM would give you a better overall performance gain than the 200Mhz extra or so you might be able to squeeze out of the chip in an overclock mod.
I used a 400Mhz 'Sawtooth' G4 before I rose this old eMac from the dead.. so truth be told, I was pretty happy with the stock 700Mhz speed, since it was significantly faster than what I was used to. Bumping it up to 900Mhz did make it run a bit faster, but it certianly wasnt a night and day difference over the stock 700Mhz setting.. at least not for everyday web browsing/code editing/eMail checking kind of stuff.. I guess I could try bumping it up to 1ghz, but I can't imagine an extra 100Mhz is going to make that much difference.
If after you upgrade the RAM to 1 GB you don't find the machine fast enough for your tastes, my advice would be to sell it on eBay, and buy something with more horses under the hood unless your confident in your soldering skills, and have the tools, the time, the eye, and the patience.
Otherwise, you could turn a perfectly functioning eMac into a doorstop.