The straight style arms were designed with stock height, OEM sway bar size in mind. See post by member Critical below
Voodoo Rear Camber Arms
Also on the G side of things
Help Rear spc camber question. - MyG37
Additional info - the OEM and SPL ones are curved. Original SPC ones are curved, then redesigned to straight for strength (probably b/c one snapped in half during track time).