timmcat,
If you are happy with the overclock and it is running stable, I would leave it where it is.
Right now I am running one of the new 90nm Athlon64 3000+s with a 425Mhz overclock on the CPU (from 1.8Ghz boosted to 2.25Ghz) and the RAM running at 100Mhz above spec. (Supposed to run at 400Mhz and is now running at 500Mhz.) I am using the Thermaltake Polo 735 Heatsink which is still running in whisper mode even with the overclock.
I know I could push it higher but it is running great and not to mention quiet, so I have left it there. If I were to crank up the Fan on the heatsink for a higher overclock, my comp would sound like a 707 cleared for takeoff.
There are good boosts in performance from overclocking. These are the 3DMark2001SE scores with the overclock:
3DMark Score 24,585
That is more than enough to run any software on the market so I decided not to push it.
Take Care,
Richard
P.S. 1.4Ghz is about the limit of the PIII Based Celeron. You would have a lot of trouble pushing it much more.