I looked at the Remington website and can't find a Model 700 with the suffix DXL. Do you have a link for that rifle? SPS just stands for Special Purpose Synthetic.
The DLX is a higher grade of gun, meaning it has alot more in the looks department. The only real difference that counts in my opinion is the bolt is jeweled, which makes the action very smooth.
For accuracy I'd go with a bull barrel SPS and ditch the factory stock, it's trash. Go with a MacMillen or similar quality stock and it'd be a damn nice rifle. Just needs good glass on top.