Not entirely positive but I believe PD11 has changed focus to the OpenCL technology. If your graphics card driver supports OpenCL, you can accelerate video effect features by using OpenCL. The key is what PD11 says in the preference area for HA. If the card supports OpenCL I believe PD11 will only display a Enable OpenCL technology to speed up video effect preview/render tick box.
On the other hand, if your computer does not support OpenCL, the wording on the HA preference area I believe is replaced with the supported hardware acceleration technology like Intel Effect Acceleration, CUDA, or AMD Accelerated Parallel Processing. When OpenCL is supported I do not believe these other options will be available in the preferences.
The above may explain why no rendering degrading is noted, in essence, you are probably using OpenCL which does not require Avivo.
Jeff