I have a pair Dekoni's Elite Sheepskin, fenestrated Sheepskins and Choice Suede pads, thought I'd share my thoughts with the T5P Gen 2s.
The sheepskins turn the bass quantity to 11 and makes them really muddy. I wouldn't recommend unless you're travelling and need the extra grunt or love overkill amounts of bass. They're very comfy despite being a relatively stiff pad, and are much better at isolating sound than the stock pad. I use these when travelling to and from work, they work well enough for that, although they do add some size to the T5P.
The fenestrated Sheepskins really don't work with the T5p Gen 2s at all. Avoid them. Bass and lower mids are just entirely lost through all the holes in the pads. I thought I accidently set a dodgy EQ at first, it was that lackluster. All that's left is treble on top of treble.
The suedes are a fantastic match to my ears. The overall sound is noticibly more spacious than the stock pads. Micro detail is somewhat improved too to my ears. The sound signature is fairly close to the stock pads. I say fairly, as my only gripe with these is there is a very slight elevation in the mids to high notes. Just at the frequency range of female vocals. Not off putting, but notciable. They do leak alot of sound, best not to use them out and about.