When I read a Platinum 8x DVD+R on my Toshiba SD-M 1612, the reading speed is 16x max. The graph in CD Speed is completely linear.
I have several 4x TDK DVD-Rs with Taiyo Yuden media code. I have burned all of them @4x. When I read them @16x max (the firmware of my Toshi is hacked), the speed drops after about 3.8 GB. The drive spins up and down and the reading process is delayed. Of course, the graph in CDSpeed does not look good after 3.8 GB. Only when I reduce the reading speed to 12x max, the graph is linear on Taiyo Yuden DVD-Rs.
So my opinion is clear: My Platinums are at least equal to my Taiyo Yuden discs. Maybe, they have worse KProbe values (I cannot test it here), but the reading performance is clearly better. The readability in standalone players (even in old ones) is just as good as the TDK discs.