nvenc perfomance on different cards

We’re trying to find the best cards for our application. It would be great to know:
Is the nvenc video engine more capable on the high-end quadro/tesla cards than the low-end cards, or is it the same on all cards? if it is more capable, how much more capable?
The nvenc sdk 4.0 application note says only two encode sessions are supported on low-end quadro cards. Which cards are these?
Some cards, such as the Tesla K10 and GRID K1 and K2, have multiple GPUs on one card. Do these cards have multiple video engines also? The GRID K1 has four entry level kepler GPUs, does it have four fully capable video engines as well?