Using my current environmental info and for demonstration purposes...
My 6.5 PRC shoots hand-loaded 147 gr ELD-M @ 3050 fps (about 140 fps over published COTS) and hand-loaded 156 gr Berger @ 3025 fps (about 85 fps over published COTS). This puts them at 1800 fps past 1000 yards (pushing 1100+ yards during fall in AZ).
Using a 127 gr LRX you'd had to run it at 3700 fps (an additional 700 fps over published COTS) to hit 1800 fps @ 1000 yards. Using a 123 gr ELD-M, you'd have to run it at 3550 fps to hit 1800 fps @ 1000 yards. Using a 120 gr E-TIP, you'd had to run it at 3600 fps (which is 500 fps faster than published COTS and 200 fps faster than published COTS for a 26 Nosler).
What are you wanting to achieve by going to a lighter bullet?