From Hodgdon's website...
View attachment 518324
Chop off 120 fps (30 fps/inch) from LRT/StaballHD/H1000/Magpro/Magnum and you're still around ≥ 2835 fps, which will just barely keep you above 2000 fps at 30°F, 29.9 inHg (sea level corrected), and 5000 ft elevation at 600 yds.
Have you seen the Badlands BDII lead free bullets?
Length: 1.505″ BC (G1): .605 BC (G7): .309 Twist: 1-8.5″ Price: 50/BOX
badlandsprecision.com
Their quoted B.C.s are significantly inflated based on my testing, but the real B.C. is still outstanding for the weight class, and would likely gain you a good bit of distance over the 168 LRX.
150 E-tip is known to be on the "slow side", so the load data should be conservative for the BDII since the BDII has a "waistline" for reduced barrel friction.
View attachment 518327
That puts you at ≥ 3000 fps with the 150 BDII in your 20" bbl. With 85% of quoted B.C. (0.265 G7), that bullet has the same energy, but an extra 100 fps over the Barnes at 600 yds.
Just food for thought. No matter how you slice it, you're new build should be a real thumper for your intended use.