The other day I received a new spindle of RITEKG04 DVD-R blanks, this time from meritline.com and with no ugly-orange logo. These appear to burn just fine at 4x.
I now believe that it is the ugly-orange Ritek media
http://www.allmediaoutlet.net/P-DVD-R-4XRitek-LOGO.html
that are at fault. As I have said previously, roughly half the spindle burned fine at 4x, but the other half of the blanks would only burn correctly at 2x--at 4x they would cause the drive to hang (requiring a computer reboot to regain control of the drive).
I have to suspect that these ugly-orange Riteks are either a mixture of American-targeted and European-targeted media, or simply counterfeits not actually made by Ritek.