SP has been used for Slim Phatty on here for a while. I have read SP used for the Sub Phatty in recent weeks. 
TE: tribute edition
LP: stage 1 and 2
What do you want to use for the slim and sub? SP for either one is confusing.
How about SLIP for the Slim Phatty and SUP for the Sub Phatty?
Hmmmnot sure provided the amount of canadian Moogers here 
How about just Sub?
I like Sub and Slim and just throw out SP. Least confusion.
I’ve heard quite a few people on Gearslutz calling it the SubP.