RAW or Theoben spring rates

They all do have an adjustable striker screw, it will make an FPS ( and perhaps other ) difference, the exact amount depends on your exact setup. A "12fpe" set up for export may need "tamper resistant" (?). The X has more head room ( pnulum ?) I believe. I have heard of adjustments as large as 60fps - bigbore- to a 12fpe rig that might change a fps or so.
Do take a look at there Facebook page if your inclined to social media. "I" don't think Martin is much into FB but he makes an effort in his "spare" time LOL.

John