Ram bandwidth speeds

In an older PC I have 3 sticks of ram running at 400MHZ and another running at 266MHZ.
Is it true that the higher MHZ sticks slow down to match the slower, resulting in less performance?the ram is:
3 sticks- 1GB PC2-6400 (400MHZ)
1 stick- 256MB PC2-4200 (266MHZ)I was considering removing the 256MB stick since that wouldn't really provide much difference in speed when compared to the other 3GB

yes its true, also you lose dual channel because they aren't matched. if you want dual channel back (doubles the speed of the ram) you need to either remove the 256MB and one of the 1GB sticks (slots are paired, remove the 1GB thats in the same pair as the 256MB), or replace the 256MB with a 1GB that matches the other 3 (speed, configuration and timings).

I removed the 256mb stick, and I will be ordering another 1GB stick soon