Not that you would notice. The drives will only manage 60-70MB/s transfer
speed so moving from 150 max to 300 max won't make any difference. The peak
transfer rate will have a higher limit, but in reality you won't notice it
being used. If your drives have NCQ, you might see a slight performance
increase*, but again, you probably won't notice.
Actually i just re-read your question and you said 'cables are SATA150'. I
didn't know the cables are rated, I assumed you were talking about a
different controller - what version is your controller, because if it is
SATA150 (and perhaps the cables came with it?), then new cables won't make
any difference at all.
* I think NCQ is only supported in SATA300, but I stand to be corrected on
this - I read this somewhere and can't find any more information to support
it!