Hold on a bit, what specific drives are we talking about here? If we're comparing two models that are the same apart from one's got the faster spin speed and faster access times, seek times etc. then yes, I'd go with the faster drive and it will make a difference. But spin speeds on their own mean nothing - a lot of modern 7200RPM drives can easily outperform older 10K ones.
It's the other figures you need to be looking at - what two drives are we specifically talking about?