It very much depends on the quality of the point cloud you need to construct, and that's pretty much related to ram. Processor will simply help you do it faster, fast clock speed and multiple cores are important, in that order. If you want high or very high quality point clouds without doing chunks on 1300 photos you're going to want as much ram as you can afford. Seriously. 512gb would not be unreasonable in your situation.
If you want to send me a sample data set I'll see what kind of quality I can get with 128gb ram on my workstation.