Well from the looks of it either one would be a good rifle to get. The XR-100 will more than likely be more expensive to shoot. The one thing I personally don't like about it, is the 1:12 twist. This will limit you to about a 60 or 65 grain bullet. With the 308 you will be able to go with as heavy a bullet that you would like to shoot. The 22-250 will be good to about 600yrds with good hand loads and a 55 or 60 grain target bullet.
The 308 will get you to 1000yrds with the correct bullet of 168 grains and up. For the 168 grain you will need a Berger VLD or the 168 Hornady A-max for the 1000yrd target. Sierra's 168 Match King will tumble at 1000yrds. Most guys that stretch the 308 out that far use 175 or 180 grain bullet for wind bucking abilities.
The SPS will be cheaper to build off of. What you will probably pay for the XR you probably can buy a trigger or a new stock for up grades. The biggest thing to think about other than budget is your optics. You want to make sure you can put the best glass on that you can afford. Either rifle will give you a great action to start from and build up from there. I see the XR is the action used for the XP-100 and there are a ton of up grades for that pistol. I would assume you could use the same up grades in the rifle action. The SPS is the classic 700 which is going to give you a plethora of options.
I'm a little confused to your just 100yrds comment, but either way, long range or 100yrds the 308 will be the more versatile rifle out of the Remington choices.
Tank
