This post took off in several directions. Getting back on topic, there is still hope for you to use the Monarch scope you have, and still get out to a decent range with the .338 RUM.
I recommend that you buy the 40 MOA Nightforce base, a set of Burris Zee Signature rings and two sets of 0.020" offset inserts. With that base and those offset inserts you can effectively dial in any base offset between about 5 MOA and 75 MOA.
If you set up the offset inserts for, say 18 MOA relative to the bore direction, that scope can get you to at least 33 MOA of bullet drop, which is equivalent to at least 1100 yds, depending on your altitude and load. That assumes a 200 yd zero at one end of adjustment, and max range at the other end.
My experience with the Monarchs is that they have more elevation adjustment than the specification says. You may find that scope has more like 35 MOA of adjustment. If so, you could push the range out to at least 1200 yds.
Your investment in rings for the Monarch would be about $75 or so, unless you already have them. The key to this scheme is knowing how to optimize the orientation of the offset inserts. If you want to go down this path, I can give you some pointers.