stupid power supply question
 

ive got a 350w power supply with a 1.3ghz athlon t-bird. the power supply cord i have is only rated at 300w. could this cause a bottleneck on my system in anyway or cause my cpu to overheat? if i run it at 1.3ghz it often overheats. (i think i have adequate cooling installed w/ 3 fans) if i run it at 1ghz it runs problem free. just wondered if the cord could be causing these problems. thnx in advance........