I do remember our conversations, kind of, that was a while ago!!! My Olsen 6-284 was also a very good shooter and also produced similiar velocity to what I am seeing with my current rig.
That said, every barrel is different and it seems that the more extreme the chambering, the larger the difference CAN be from barrel to barrel. Lilja barrels are not known for extreme velocity potential because they generally run pretty tight on bore diameter. This is because they are ment for BR type rifles more then anything so when you get a slow Lilja, it can be pretty slow but generally very accurate.
You did not mention if you could push a bullet though the neck of a fired case. From your numbers, you should have plenty of room for proper bullet release, in fact a bit more then I would recommend.
That said, if you have not confirmed this by making sure you can push a bullet through a fired case I would do so. The older a reamer gets, the smaller the neck and throat diameter get. This is just normal wear. I have no idea how many chambers have been cut with his reamer but I bet its more then a few!!!
Never hurts to make sure and if needed, take a slight turn off your neck diameter if needed. A neck that is to tight can cause some SEVERE pressure issues.
Anyway, I would confirm that and if that is not a problem, I would say your about there with your load development. With conditions as bad as you were shooting in, you got very good accuracy results, good loads, good rifle and great shooting!!!
Unfortunately, the 6-284 is one of those wildcats that are just not well suited to alot of load development as you well know. Kind of like the top fuel dragster. To many runs down the 1/4 mile stip and things will need to be replaced!!! But man those runs are FUN!!