I love this question! And no, I'm not being facetious. I see this exact question all the time on a hunting forum and FB page all the time out here in Arizona and I can promise you that you will get answers all over the board and everyone has their opinions as to why they are more right. Since you included, moose, though, that changes the usual answers quite a bit. The 6.5-284 Norma and 6.5 Creedmore are very popular long range cartridges for all but moose out here. Maybe its because I've been following it more this year than in years past, but I've seen more Coues whitetail (our little whitetails) taken at 600-1,000 yards and several have been using the above. If you are interested in checking out any of those discussions on local forums, let me know and I'll get you the links. They get quite laughable at the obvious internet chest pounding and overt testosterone rivers!
Since moose is in your plan, I would recommend any of the following: .30-06, 7mm mag, 7mm short mag, 7mm STW, .300 Win Mag, .300 WSM, .300 RUM, .338 Win Mag, and (if you are feeling really crazy and have deep pockets), the .338 Lapua Mag or .338 Edge. Every single one of those will effectively and humanely kill all that you are seeking at ranges well beyond what you seek. Before you or anyone else laughs at the .30-06, remember that it is the most popular hunting cartridge and comes in the widest range of bullet selection, especially for handloaders. I know of several elk that have fallen to a 165 gr or 180 gr bullet fired from a .30-06 at 400-700 yards (unfortunately, none were mine). The bottom line is going to be whichever of those above you shoot most comfortably. If recoil is an issue, there are certainly ones to stay away from (or have a brake put on). I won't do a side-by-side comparison of the pros/cons of any of the above and, by no means, am I claiming to be the know-all expert, but I do live out west, hunt out west, and shoot out west quite often. All of the above have their pros and cons and I encourage you to research each one for just that. When you figure out what you want, I see most all of the above for sale on one particular forum regularly and can help you. Most come with good scopes.
As for the scope and bullet/load issue, that's another one where you will get all kinds of chest pounding about which bullet weight/brand is the best and which scope has the best quality of glass. I will say that, in order to do it right, you will end up paying as much, if not more, for a good scope than you will your rifle. As for bullets/loads, you can get all kinds of information above, per the chest pounding, but, in the end, you have to find the right combo that your particular rifle likes. Handloading gives you many more options, but if you lose your ammo en route, you can be royally screwed.
