The .300 win mag barely has a better long range trajectory than the 6.5 Creedmoor. It's got more punch for hunting obviously, but as a target rifle it wouldn't be a high choice for me. Too much recoil for too uninteresting a trajectory.
Typically if you're stepping up past the 6.5 Creedmoor, you're going to be looking at something with a bigger case in either 6.5 or 7mm. So 6.5-284, .280, .264 Winchester, 7mm Remington Mag, 7mm SAUM, 7mm WSM. Somthing like that.
There are more options farther up the power ladder, but those are pretty standard options. I excluded things like .30-06 and various .30 and larger magnums that really can't outperform the 6.5 Creedmoor, 6mm Creedmoor, or .243.
What you might choose depends heavily on whether you reload. Some of these calibers have next to zero factory support.