L1 in rs500 and 3 door,
L6 in 2wd saph,
L8 in 4x4 saph
P8 in big turbo escos
EECIV in small turbo escos


the L8 and P8 are interchangable but not the chips, the L1 and L6 are interchangable but no the chip, the L1 and L6 use a different throttle position sensor than the L8 and P8,

basically, the P8 over the L6 has more memory and can perform more things like, closed loop boost(with overboost) and fuel control, antilag, water injection etc etc

but for a normal car, i reckon you would be hard pushed to notice a differnec in teh way the cars drive if they are both setup correctly.