I saw these two packs.. Stormer hobbies say the MAh is "slightly" ( 200mah) lower so lower runtimes.

is there any other difference other than the mah?

SMC Batteries 5200mAh Lipo Battery, 7.4v 40C Sport Pack 109.99
SMC Batteries 5200mAh Lipo Battery, 7.4v 40C 129.95

Not much information other than what i already said here on the stormer hobbies website and the SMC website isnt any help.

I plan to use it for Racing my Slash so being a "Sports pack" should not matter?

The sport pack will work fine in the Slash. I believe the only difference is the Sport Pack is not matched by SMC. The vast majority of packs on the market are not matched.

will that pack fit in a XXXT CR without Mod. the battery tray?

Yes it will

thanks hankster!