1. I would go with a variable for sure. Fixed powers are too limiting for close up shots. Plus you want something with either a BDC type reticle or target turrets that are easy to adjust if you plan on working out LR.
I do like the Nikon scopes though and with a little work, the ones with the BDC will work out to 600-800 on deer size game, particularily with a 270. You just need a ballistics program ($70) to figure actual drops for each circle at 2 or 3 powers and make a credit card size laminated card to carry or put on side of stock or scope. Go with a 200 yard zero at the X and you will find each circle at max power will be about another 100 yds plus or minus 25-50 yds.
I have a 3-9X Kahles TDS reticle with my 300 WSM
that can go from 317-840 yds by using 6, 7, 8 and 9X and the first crosshairs below with a 200 yd zero. I have about 40 yd increments by switching power and lower crosshairs.
2. IF you are going to shoot LR the scope either has to have lot of elevation or you use a tapered base. Just because a scope says it has 40MOA of elevation, that does not mean it will automatically center. You might find it is way to the top to zero.
Recommend you look at a double dovetail base with burris signature rings that allow you to add inserts if you need the MOA. The double dovetail is solid weight is not an issue here anyway. Talley rings are noted for lightweight guns, which is not what you have. IMO the double dovetail with burris signature rings are a solid, cost effective setup that you will not regret.