[Amps] 4CX5000 in Grounded Grid gain??

[Markku Oksanen]

ALL
I managed to get my hands on a couple of VERY used 4CX5000 and the related parts.
Although I have build a couple of tetrode (gu84b) amps grid driven, this tube has quite a different demands.  In grounded cathode, neutralizations seems to be a must.  And perhaps IMD is not the best this way either.  SO, I am looking at using this tube in grounded grid.
I read  Tom's (W8JI) infor on the topic http://www.w8ji.com/grounded_grid_amplifiers.htm, however I have not been able to find a way to estimate gain accurately.  Most sources and my early experiences with a GC tetrode amp talk about 9-11 dB gain but how this is calculated is a myth, even after trying the formula from Tom's page.
The tube, with parts from an old transmitter, would run at 7200 V on the plate, I have transformers to choose the grid and screen voltages to suit the design.  Also choosing these needs some help for GG use.
This is naturally for a SUPER ROBUST auto-tune amp for contest use.
I would really appreciate help in finding the correct theory to get my design going forward.
Markku