Which's better - Higher speed,less ram or more ram,slower speed?

I have a Hynix 256MB @ 266 MHZ and just added a Kingston 512 MB @ 333 MHZ memory module which adds up to 768 MB @ 266 MHZ (It stepped down to 266 MHZ automatically). Question is which will give a beter performance. 512 MHZ @ 333 MHZ or 768 MB @ 266 MHZ? Or it depends on type/and or number of applications I'm running ? I'm using XPHome SP2 with P4 2.8 GHZ Intel 845G Chip

It depends on the usage profile, yes.