Currently using 243Win. for whitetail deer in NY - you will find the 7mm Rem.Mag. to be
more effective, assuming good hits/shot placement, but also with much more recoil and
muzzle blast, and more expensive ammo. 7mm Magnums are really not needed for
whitetail. It's a good cartridge, but just really more than needed.
You would probably be better off looking at a rifle chambered for either the 280Remington or the 270Win.. If you're a handloader, I'd recommend the 280Rem.
If you're using factory ammo I'd suggest the 270Win. as it will not only have good factory loads for deer, but the 270 also has a varmint load (100gr. from Remington).
Of course, if varmints are not on your agenda, then, again, I'd go with the 280Rem.
which is a 7mm, just not a magnum.
There's really not a whole lot of difference between the 270 & 280 as the difference in
bullet diameters is only .007" (270 = .277" and 280/7mm = .284").
The 7mm Mag. will give you a little more range/flatter trajectory than either the 270 or
280, but as noted above, there's a price to pay (rifle weight - generally heavier/longer,
muzzle blast, and recoil). Do you really need to shoot at deer at 300 - 400yds.? If not,
go with a 270 or 280. AND, keep the .243 for varmint use, and as a backup deer rifle.

Another consideration is availability of rifles for the 270 or 280. Most all manufacturers make rifles chambered for the 270, often in several different models. The 280, good as it is, is not quite as popular, and your selection will be more limited.

My personal choice is the 270Win. 'cause of the availability of a factory load for varmint use, as well as a greater variety of factory ammo for big game hunting.

Whatever you choose, don't rush it. Take the time to do some research on the Internet,
read some books/magazines, and talk to others at the gun shop or on the range.

Here's a link you might find useful: http://www.chuckhawks.com/index2.guns.htm