Default [Q] I'm trying to find the correct ROM

I have Samsung Galaxy Tab 10.1 GT-P7510MA. As I look through the various ROMs for my tablet I see "p4" in the description e.g. p4, p4wifi etc. Can someone explain what "p4" is, and what its implications are for finding the correct ROM? I'd be grateful. Many thanks!

Additionally, should I use a TWRP or CWM, and which one of those? I am incredibly grateful as you help me grow out of being a 'noob'.