A small problem!

Hi all. I have a Mac Pro Intel 1st Gen. (quad). My computer has 4 Hard drives with one of them being the latest adition and empty. Lately the boot up time is geting longer and longer. I tried almost everything, from the Software side (cleaning-permissions-rebuilding) and the Hardware side (running tests on my hardware-no erros) to no avail. It is still booting up slow. It was suggested to me that my Hard Drive that has the operating system (it is the boot volume) is tired. It is the one that came originaly with the computer so it is 7 years old I guess. I was thinking of doing a fresh install of my Lion in my empty new HD and then move the programms I need there. I need your help to advise which you think is the best way to do it (I do not want to use my back up as I might have software problems in the current configurtion) and also if the boot drive needs to be in slot number 1 or not.

Your help and advise will be much appreciated.