How old was the plug? Are you running a 9 or an 8 plug?
They don't last forever, so an old plug could have contributed to the fouling/loading up. If it was a new plug, I'd probably start with the aircsrew at your new position of 2 out (I guess you were 1 3/4 when the plug loaded up).
If hours of constant idling and low rpm at high altitude is not your normal riding condition, I would not jet to optimize the bike for that situation.
If it was otherwise running great besides loading the plug up after hours of just off idle, you can't be far off.
Personally, I think it is nice to have a little safety margin, especially if you go on long rides where weather and riding conditions may change alot during the day. For example, if you jet it to run perfectly crisp for low rpm rock crawling at 6,000+' elevation, 80* temps at noon, are you going to be too lean when you leave camp back at 8:00 am, 4,000' elevation and 55* temps?
It's always a compromise, so it's best to err on the side of more fuel. Sounds like you are in the ball park now. If it were me, I would put in a new '8' plug and leave the airscrew at 2 out, then go for a ride.