Postman, like JeffK, I have a Ruger No1 in 500NE. I used Graeme Wright's load of 106gn AR2209 (H4350) it got to 2200fps in my rifle - but I have a 30" barrel & run BP thru it as well.
It torqued quite a bit in my rifle so I decide to try AR2208 (varget) instead.
I got to 92gn (Hornady brass, Federal 215 primer & 570gn Woodleigh softs)for around 2160fps, it doesn't kick like the heavier 2209 load, but as I have a lot more safety up my sleeve in regards to action strength I would back off this load by at least 5 gn & work up from there.
I would get Graeme's book "shooting the English double rifle" as it was invaluable for full nitro loads, Nitro for black loads & Black powder loads (including duplex BP loads) for the 500NE.
It give great advice in regard to regulating loads & what to look for - loads too fast/too slow etc.
He doesn't state any full AR2208 loads for the 500NE, but if you get a mate to check for you use Quick load or Load for a disk start at the lower end & work up from there; a simple powder change can make a huge difference in grouping.
Sorry mate but unfortunately I didn't keep any lower data on my work up to my full AR2208 loads.
Graeme's NFB load of 72gn AR2208 behind the 440gn Woodleigh (wad needed)& 215 primer is amazingly accurate in a mate's Sabbati double! I use that as a pig load.....great splat when it hits!

All doubles have a sweet spot, you just have to find yours - but I would recommend the Woodies as they are designed specifically for the old English calibres.
It will be worth it in the long run mate, to get a double to regulate is the ultimate in reloading!
All the best mate - keeping my fingers crossed for you!
Cheers
93x64mm