I'll still be very surprised if an overclocked AMD 6400 will get anywhere near an overclocked 6600....across the board, maybe in the odd test, maybe even almost in Sceincemark 2 but then thats as much the memory and HDD access time as it is the speed of the chip. I know Trt's old 6000 beat a number of C2D's in sceincemark but as I said, because there are so many variables in that test the ones he beat probably were running their memory at 800-900Mhz, Trt's was running around 1160Mhz and in that test thats a HUGE difference, you only need to look at the SuperPi times, the 6000 @ 3.5Gig was hitting just over 23 secs, the C2D @ 3.5Gig were hitting near to 14 secs!
Bottom line tho, for those AM2 owners who are waiting for Phenom, it is at least an upgrade path, whether it's worth it or not is another matter, IMO unless the 6400 can give you 200Mhz overclocked on the 6000 then it's clearly not worth it and TBH I cannot see a 90nm chip doing 3.7Gig, today, tomorrow or even when the pigs fly!