Celeron, I honestly don't know what the facts are with your Pioneer "05" model, since they curiously stopped listing that speed CLV/CAV specification that you see with the "04" model. I'm just trying to bring in some other issues to be aware of depending on what you are trying to do. Burning video is typically CLV, and Burning data is typically CAV (as well as reading it).
If you look at that link for the 04 model it does say that model
Writes DVD-R @ 2X CLV, 1x CLV
which is typically the one used for Video, and it would be reasonable to assume that the CLV is the same for the new "05" 4x -R writing, and should work for burning Video if you have compatible & 4x rated DVD-R media.
But there are so many factors besides the obvious +/-R, +/-RW media types and speed rating, and burning a given type of media with a given type of burner.
There are motherboard versions, firmware, Ultra DMA settings, hardware master/slave setups in conjunction with your other Primary/Secondary IDE drives, issues involving the correct type of IDE ribbon and position of Master/Slave connectors on the ribbon, Burner firmware versions, type of operating system (XP vs. Win9x) file system (NTFS vs. Win32), software program (NERO, etc.) defaults like the "verify-on" possibility.
There are also different performance speed ratings between a given DVD or CD burner and a specific brand of media. You cannot ask for advice with a type of media if someone has a different burner than you. It will be much slower if you try to copy DVD or CD "on the fly" instead of first reading to Hard Drive, then separately HD to Burner. (Ultimately that way does take longer because of the complete read, then complete write from HD...but it is the only way to go.)
I hate to also tell you that even with a given type of media, and burner it is well established that the burner hardware model and media (especially CD media), that when & where a particular burner model &/or type of media was made will affect it's actual speed rating.
If you are doing things on the PC while it is burning, it may be causing packet writing errors that have to be auto-re-verified during the burning process that can slow it down....assuming you have a decent speed HD & the correct speed rated (66, 100, 133) IDE cable.
You need someone to come here and say they have almost the same setup in most of these ways as you, and using the same media to really know. As a suggestion, I would recommend buying a couple of quality brand-name DVD-R 4x rated media and see if you can rule out one of the more common issues ('El Cheapo media") before you jump the gun and start assuming it's your burner.
You got one of the best rated Burners.....why grab a no-name media to start with?