If you want something flat along those lines...

.270 WSM or 7mm WSM

maybe a 6.5mm-284 if you reload, maybe not super flat, but super accurate, it's the 1000yd goto so it seems.

Get a .270wsm and top it with a zeiss with the z800 reticle. Zeiss also makes areticle for the .308 out to 1000yds I believe.

If you're considering the .308, how about the .260 or 7mm-08?