Bubb, if staying inside 1000yds, there are a lot of possibilities from 6.5, 7 and 30cal. The first part is making sure that you have an accurate rifle and scope. Most good production guns with a little tuning will work. All you need is consistent MOA performance at long range.
Take the time and look through as many scopes as you can. You need clarity and resolution, with reliable adjustments. Lots of mag is not necessary (10to 16X is all you need).
You have to be able to range so a laser rangefinder is next. I would look for the Leica 800 as they are on sale now.
Barrel length. Decide if this is going to be a portable or bench rifle. The longer and heavier the barrel, the better- free performance and reduced recoil. The longer the barrel, the smaller the case to get the same performance. Or, more performance from the same case.
NOW we get to the cartridge. You have to be able to afford to shoot this rig so look at bullet/component costs. Reloading is a very big plus.
For deer, a fast 6.5 or 7mm is plenty. 6.5-284, 6.5-06 stand or AI, 6.5WSM are all excellent. 3000fps with a 142gr MK or Amax will be plenty out to 1000yds.
The new 270WSM may just be the ticket with 140 or 150gr SST bullets.
In 7mm, the 7WSM/Rem mag, 7Gibbs, and even the STW (???) are excellent choices. The 162gr Amax or SST at 3000fps will be a tough combo to beat.
In the 30cal, yes, the win mag and WSM are great choices. 165gr 180gr SST or Amax, equivalent MK will all get the job done when launched around 3000fps (see a trend here?).
I am very partial to the 30Gibbs (improved and modified 30-06). Getting performance very close to the WSM (identical to the RSAUM) without the bother and cost. Mine is on a Parker Hale action and a 26" barrel w/muzzle brake
. With a B&L 6X24 4000Elite, it tips the scales at 10lbs. Still light enough to be portable, yet has the moxie to reach out as far as I can range with my Leica 800.
As you have already read, you need to get the bullet into the boiler room and any of the above will have enough oomph to take deer. With these easily expanding bullets, as long as you have over 1200fps at impact, the bullets will work.
Practise, Practise, Practise. That is the real difference between success and failure. All the equipment in the world is not going to help you dope the wind or know how to follow through.
As to amount of "energy" to kill a deer, ask yourself this question. If you held a handgun in 45ACP/9mm luger/38 special against the ribs or shoulder of a deer and pulled the trigger, would this kill the animal?
I hope you answered yes. Look up how much vel/energy these cartridges put out. Makes you wonder.
So, is the RUM necessary - NO. However, if you already have one, then you will not need to rebarrel or get a new rifle when you are ready to go further out.