GUID or APM Partition for Snow Leopard Upgrade?

I now realize that the prefered hard drive partition for Intel Macs is GUID, however, when I installed my current boot drive to my 2008 MacPro, it was partitioned with Apple Partition Map. I am now at OS 10.5.8 and plan to upgrade to Snow Leopard (moving very slowly on OS upgrades as I have a lot of legacy software that I don't want to lose functionality for). I have not experienced any problems with present APM configuration running 10.5.8 on this MacPro.

So, to the point: can I directly upgrade to Snow Leopard with my main boot drive still partitioned APM? What are advantages of using GUID? If needed, what is best way to convert drive partition to GUID (I assume it involves a backup, repartition of drive, followed by restore via a disk image)? I have used Carbon Copy Cloner for creating disk images for many years, but don't know what new may be out there ... any thoughts on best utility to accomplish this task?

Thanks in advance for your thoughts!