Heat and humidity are both factors in the performance of the drive. Why else would Plextor (and every other maunfacturer of electrical equipment) have a range of acceptable operating conditions for both temp and humidity in their manual. It ain't there to spend money on ink!
I completed part of my testing on my new 716A and Benq DW1640 and will be posting the audio cd results shortly. As to this discussion, here are a couple of PxScans of Taiyo Yuden 48X CD-R's burned at 16X on the Plextor. The first series was done in the morning when room temp was approximately 78 F and humidity relatively low. The second was done with room temp 90 F and significantly higher humidity the next day. The computer had been left on all night and day since the first burn. Temps at the CPU heatsink/fan by external probe ranged from 28.5 C to 34.5 C. My GeForce 6800 Ultra temp per nVidia display states current ambient temp 41 C and 57 C GPU core temp. A temp probe on the exterior of the video card's heatsink reads 37 C currently, but there is a 120 mm fan on the side panel (four 120mm fans altogether in the case) blowing air over the card, so take these readings with a grain of salt.
Bottom line: Best burns in cooler, lower humidity conditions for the Plextor. Interestingly, the BenQ may perform better in more extreme conditions compared to the Plextor from my very small sample so far.
Picture 1: Fuji TY 48X CD-R Audio CD Burned 16X Plextor PxScan - Low Heat/Humidty (Reference point for Nero Quality Scans)
Picture 2: Fuji TY 48X CD-R Audio CD Burned 16X Plextor Nero Disc Quality - Low Heat/Humidty
Picture 3: Fuji TY 48X CD-R Burned 16X 716A Nero Disc Quality - High Heat/Humidity
Picture 4: Fuji TY 48X Audio CD Burned At 40X In BenQ Nero Disc Quality - High Heat/Humidity