The .30-06 is such a well balanced round it really is hard to do anything better than it without stepping into a "magnum" round. I think there are a lot of standard chambers out there that match the 06 in a lot of ways but few are as flexible as the 06. My two favorite non 06 cartridges are the .270 Win and .338-06. I've tried most of them as I own or have owned the .25-06, 6.5-06, .270, .280, 8mm-06, .338-06, and .35 Whelen.
If you want the roughly same power as a .30-06 but flatter trajectory you're going to have to look at something like the .270, .280, .280 AI, or 6.5X284 for non wildcats, and the 6.5-06 or AI in but they are a hand loader only cartridge. Again the .30-06 is going to take over long range if you are using 180 grain or heavier bullets but you won't notice it until you are way past 500 yards.
For cartridges that are going to hit with more energy and bigger bullets at normal hunting ranges <400 yards you have several to choose from as well. .338-06, .35 Whelen, and 9.3X62 are all standardized cartridges and you can buy factory ammunition for them. For wildcats you have the 8mm-06 and you can AI version it as well as the the .338-06 and Whelen. I've never seen a 9.3X62 AI as I think the cartridge has a little steeper shoulder than the 06 anyway.
The .338-06 can do what you want but the .30-06 will eventually take over before or at 500 yards. With Hornady 200 grain bullets you can push them much faster than a .30-06 and you can push 225's about the same speed that an 06 pushes a 180 grain bullet. Hornady list the 200 grain bullet at 2900 max load and 225's at 2700 fps. I've got some 180 Accubonds to load up as well and I imagine I'll push them right at 3000 fps pretty easily out of my .338-06.
In wildcat rounds you have the Hawk, PDK, Gibbs, and too many others to mention cartridges that all provide more thump and speed but only marginally and still based on the 06 case. Most of them have the shoulder blown forward creating a much shorter neck and in standard length barrels only gain 100-200 fps over their standard counterparts. The Gibbs cartridge was designed to use a 26" barrel as measured from a loaded chamber not the breach face as most other barrels are measured.
If you want the roughly same power as a .30-06 but flatter trajectory you're going to have to look at something like the .270, .280, .280 AI, or 6.5X284 for non wildcats, and the 6.5-06 or AI in but they are a hand loader only cartridge. Again the .30-06 is going to take over long range if you are using 180 grain or heavier bullets but you won't notice it until you are way past 500 yards.
For cartridges that are going to hit with more energy and bigger bullets at normal hunting ranges <400 yards you have several to choose from as well. .338-06, .35 Whelen, and 9.3X62 are all standardized cartridges and you can buy factory ammunition for them. For wildcats you have the 8mm-06 and you can AI version it as well as the the .338-06 and Whelen. I've never seen a 9.3X62 AI as I think the cartridge has a little steeper shoulder than the 06 anyway.
The .338-06 can do what you want but the .30-06 will eventually take over before or at 500 yards. With Hornady 200 grain bullets you can push them much faster than a .30-06 and you can push 225's about the same speed that an 06 pushes a 180 grain bullet. Hornady list the 200 grain bullet at 2900 max load and 225's at 2700 fps. I've got some 180 Accubonds to load up as well and I imagine I'll push them right at 3000 fps pretty easily out of my .338-06.
In wildcat rounds you have the Hawk, PDK, Gibbs, and too many others to mention cartridges that all provide more thump and speed but only marginally and still based on the 06 case. Most of them have the shoulder blown forward creating a much shorter neck and in standard length barrels only gain 100-200 fps over their standard counterparts. The Gibbs cartridge was designed to use a 26" barrel as measured from a loaded chamber not the breach face as most other barrels are measured.