Put the clockspeed at it's standard settings and just go 5Mhz up every time when overclocking, and test it for a while, if it's still stable then add another 5 Mhz and so on......
You should be able to get around 25-45Mhz extra clockspeed, but this depends on your system.
I got an extra 35 Mhz out of my Savage 4.
By the way what utility are you using for overclocking?
I have Creative SAVEGE4 and I am using creative lab software that came with the card. It has a max. of 143MHZ. Have you run 3DMARK 99 MAX with your card? I have 400MHZ AMD II and the last part of demo where you walk in the hall ways ... it gets a bit choppy. How about yours?
PC133 128MB ECC
WD SCSI2 10K 5.2ms 18.3G
Vortex2 w/ digital out
Sony MHC-5500 Digital Signal Processer - 30 equalizers and Dynamic Sound