I tend to agree with Sheridan on this one. Quality optics with enough magnification and enough resolution to actually see what you're shooting at will go a long ways.

In general, since most predator calling is either dusk or dawn, I'd also agree with the 44mm recommendation, or a 50mm with a raised cheekpiece (not hard to make your own, or several quality aftermarket models are available). I run 50mm scopes on as much as I can, plus a couple 56mm Nightforce scopes. Yes, you can tell the difference in light transmission! 30mm tubes count for a lot in the way of light transmission as well. I'm a leatherworker, so I made my own cheekpieces, but some of my buddies just use those elastic buttstock shell holders ($10) plus a few shims of trimmed foam rubber, leather, etc etc to allow proper cheekweld for these taller optics. (Or you could just shoot a scoped A2 a lot like I used to and get used to shooting heads up with a "lower jaw weld" instead of a "cheekweld", haha).

Great rifle choice. Personally, for that rig, I'd look into a Leup VX-3 LRT 6.5-20x50mm. Scope runs about $900, well worth it. The OTHER option I'd recommend would be the Bushnell Elite 6500 4.5-30x50mm, about $850, but has fantastic versatility. A 4-16x44 or 6-24x44mm are also good options, but these are hard to find with enough internal adjustment for my tastes. However, since you're limiting your shots 0-250yrds, you'll be able to easily estimate proper hold over, rather than dialing in your turrets. You could pick up a $500-600 scope like a Vortex Viper PST 4-16x50mm, Nikon Monarch 4-16x42mm, Leupold VX-2 6-18x40mm, etc etc, but ultimately, you WILL notice a difference. The Leup VX-3 LRT is a very hard scope to beat, especially if you're strapping it on top of a heavy barreled Kimber pushing .204 Ruger.