With retumbo and the 215, I was at what I would consider a max load at 2990ish average, from a 20". Best accuracy in a ladder test would have likely been around 2900ish just judging from how I know this rifle. A 245 would likely be mid 2600 to low 2700 in my 20" for accuracy, just guessing. Add around 40-60 fps for a 22". That is with a .215 freebore....if you ran a longer freebore specifically for the 245 you could maybe do a shade better. So 2700-2775ish would be my guess for an accurate load with retumbo, a 245, and a 22". Take away probably 30-50 fps for H1k. Add it back with a longer freebore. Add 75-100ish fps and half the barrel life for N570.
Me, I'm just running a 190ish grain mono with a bc near that of a 230 berger at 2950-3000 from a 20" using Retumbo. It's nicer on my shoulder than a heavier bullet, and I'm not pushing pressure either. Lovin it.