the 24 pin is a new type of connection,your getting the same results using the sep 4 pin,if the pc is stable then I don't think you should worry a lot of cheaper power supplies last for ages and work fine,but you get what you pay for and more expensive higher power psu's do offer more stable voltages
you can buy molex splitters for pence
http://www.blankdiscshop.co.uk/acatalog/pccables.html
I use a couple of these with a reasonable 500w psu (not an expensive one) and my machine runs 8 hdd's and 3 optical with a x800 xt pe fine and dandy