A 22BR with 70gn bullets is what I use for 90% of my F class shoting. I had a BRX shooting 90gn ( and even 105gn) bullets and it was good, but barrel was only 20" long so velocity was low. I still occaisionaly use my 22BR with fast twist barrel with 80gn bullets and when it was new, it was great, my favourite.
I love the 22BR and have done very well with it up to 6-700 meters and occaisionaly get lucky at 800 meters but it starts to lose it a bit at 1000yds, getting more verticle and blowing around a bit. I have used it in a very windy shoot at 1100 yds where I came 3rd, but I was realy having to hold off a lot. For 600yds, lovely cartridge, for 1000yds, I would rather do what I have just done, neck it up and blow it out to a 6x47.