I have the RL 23 but no N570. I have been looking for some local tho maybe some will turn up. Sounds like it is working well for you. I use the 23 in a couple of other rifles so I keep it on hand.My barrel is till about a week out so I can't even try it yet.
In my 6.5 Sherman Short I'm starting to use R23 with the 130 Scirocco. I'm getting 3275 'ish with no pressure at 80 degrees. 56 'ish grains with the 140's gave me near 3200 but 57 hit pressure signs. Those are in a 26" barrel. R26 gives good velocity but I'm not convinced if it's temp stability having used it in my 6.5 WSM. N570 gave good velocity and accuracy but it was pretty compressed. H1000 gave great SD's but not the velocity I wanted. H4831SC gives good velocity with the 130's.
All that is in the Sherman Short but, I'm sure, it can be translated to the Sherman in some way.
I am sure that with the size of the case being bigger that the regular Sherman should use more powder. I have been talking to a few people and think I will start out fire forming my brass with 23 at somewhere around 57 to 58. I haven't decided yet what I am going to use for fireforming as far as the bullet. I have alot to choose from. From 107,120,142 SMK to 123, 129, 147 Hornady. Probably 107,123 or 129 since I don't use these in anything else anymore.