Actually, the Seasonic S12 430 with 29A on the 12v rails is more than enough for the system even when overclocked.
C2D E4300 OCed to X6800 speed (2.93GHz).................66w
CPU Power Consumption Link
Radeon X1950XTX........................................................125w
GPU Power Consumption Chart Link
1 Hard Drive..................................................................12w
1 DVD Drive...................................................................12w
2 120mm Case Fans at full speed..................................12w
1 120mm CPU at full speed............................................6w
Total max power consumption on 12v rails.....................221w
Total max amp consumption on 12v rails......................18.42a
Note the X1950XTX uses slightly more power than the X1950XT.
That leaves more than 10amps (or 120w) on the 12v rails yet to be used.
Assuming linear CPU power consumption in relation to clock speed, for every 300MHz above the speed of the stock X6800 CPU, add another 8w to the power consumption.