I just did this upgrade this past Saturday. I didn't have time to run a full benchmark suite, but I ran a quick 3Dmark05 and also ran BF2. BF2 with 1GB of ram (all settings on high, 16x12, 4x/8x) chugged like a mofo for the first minute or so like always. Installed the other 2 sticks, booted back up at the 333mhz 2T. BF2 now ran like a dream. Not a single stutter. Night and day, truly. Ran 3dmark05. No difference in score at all.
Still trying to tweak the settings though because I am unable to overclock to the exact settings I had prior to going 4 sticks. I was at 300 * 8x with a /133 divider. I can't get past 2250 at the moment. With a little more testing, I'm sure I'll find the right settings.