After tweaking my test rig to fit a variable supply for fixed bias, I proceeded with the tests with the EML20AM valve. 
After playing a bit today with the valve, found that it picks up hum like the Ba or any mid-mu valve due to the large grid which acts like a proper antenna. If you screen the valve is dead quiet. I used the same rig test with a CX301a to compare and definitely the 20A picks up more induced noise from the workbench.
The H3 levels are higher than I’d have expect, about 7-8dB difference with H2. The harmonics have a nice waterfall shape which is good and THD shows how linear the valve is, very nice. You get only 0.08% for 40Vrms. Didn’t test further but I expect it will perform really well:
As a driver is outstanding. You won’t find many valve out there this linear capable of swinging 40-50Vrms with just THD below 0.10%.
If you need the gain as your system is only one output stage (like mine) then this valve is a good option. With a step up transformer of 1:2 or 1:4 can make a very nice DHT driver for a 300B/50/211, etc. For larger swing volts I’d probably look at biasing it above 220V, albeit it can work very well there. The anode current above 15mA makes the stage able to manage the output valve’s capacitance without any slew rate distortions.
Here is a quick snapshot of the frequency response using the gyrator load:
