Actually the reports of slow converting/burning are exactly what I have always encountered with Toast Titanium 11 (latest version and previous).
I have experienced time and time again it taking hours to convert/burn an M4V to a disk. As previously mentioned I now NEVER burn straight to DVD anymore - too many ruined DVDs when Toast screws up on the burn.
My hardware is a MacBook Pro with 8GB of RAM and I ONLY run Toast when I am converting/burning - otherwise it is even slower. What frustrates me is that I have used Apples advise which is to ONLY have the internal hard disk connected (no externals) since the system slows down to the speed of the slowest peripheral according to Apple. I have worked on this problem over and over and simply put Toast is excruciatingly slow and does not use the available resources such as all the CPUs that are open to it.
Your experience is not unusual if you ask me - somewhat disappointing - if only Handbrake could be used to burn DVDs since it is far far faster and takes advantage of the entire resources of the system to do it's job.