"accurate at distance "
If you are accurate at the distance you want to shoot then the .270 is more then enough. People take large game with smaller calibers every year. There are also people out there who loose smaller game (hogs, deer, etc...) with large calibers. So again, as you stated, accuracy is the key.
You mentioned you wanted a flat trajectory. Ever think of the Weatherby Mag. line? There are some excellent rifles there with renowned flat trajectories. The 7mm mag and .300 mag come to mind.