I too have been playing with grid chokes. How many henry are your grid chokes and what size is the coupling cap? Due to the rising impedance of the grid choke I'd expect a gain rather than a loss of HF.I have not tried nor confirmed but I have been told that the grid choke would not work well with a CCS or choke loaded driver. If one looks at "historical" amps you always see a "R" in there someplace...like LCR or RCL. My grid chokes will also be replacing 220K grid leak resistors. I am going to use RCL coupling and will try 0.47uF cap first...if I have a bass boost I might go up to a 1uF cap or perhaps play with a resistor in series with the grid choke (I'd like to avoid a resistor across the grid choke). I am now obsessing about where to place them (four of them) in my chassis as I hear they are prone to picking up noise.
Russ