Sorry to weight in here - I use a single stage parafeed 801a amp on some compression drivers. Mikeys Exo 45 transformers - following gordon rankins advice I use 5k transformers with the 801a choke loaded running at 400v/40 ma/-20v. Sounds super clear with a fantastic midrange. "flipped" B7 15 k at the input.
At your operating points of 325 volts and -27 bias it looks like the 801 a is running at about 15 ma from the curves . The combination of a 27 k resistor and a 10K transformer gives an effective load of around 7.3 k - I suspect the 801 might like a little more current at this load - you will probably need more B+ but it would be worth exploring if you can
800v should give you 20 ma?
801a parafeed is the best of maybe 20 amps I have built
Simon