T9.5 as unholy

Is there any dk that actually plays with t9.5 as unholy over the t10.5 and is it tested as how it behaves at all? The idea of the set is to make wandering plague hit hard from blood plague crits.

It is good if it boosts your progression until you get t10 sanctified/heroic.
But to use it if you have t10 or go out of way to get it... no.
In some situations it can pull ahead with very questionable "usefulness", its just not worth it.

Another question if lets say you do icc 25 and you get 3 unh dks in the raid, the Ebon plague debuff from each dk stacks , or overrides eachother ?

Max you can get is increased 13% magic damage done and 30% disease damage done - it is not stacking, also Curse of elements and Earth and moon will not give any additional damage. You can have 10 warlocks, 10 boomkins and 10 unholy dks, you still get maximum 13% bonus magic damage.

i was more conserned about the disease damage, the magic damage i know it doesnt stack , before atlaest the ebon plague debuff stacked

Tested both.

Only fight in which T 9.5 can be better is Halion 25m hc Phisical Realm, where u constantly get adds that u have to kill.
Its ONLY good for Adds DPS, aka constant AoE DMG.
Ur single target (boss dmg) dps will suffer a lot tho, and u will always do less DMG overall VS a T 10.5 Unholy DK, even on Halion duo to P2 where ur T 9.5 bonus cant shine...
On top of that Death and Decay is far more superior than diseases when it comes to AoE DPS and it will do less DMG with T 9.5. So even on bosses which u have to AoE DPS from time to time (LK 25m hc P2 with valks) T 10.5 will win in the end.

Overall, u get far more and better stats while using T 10.5 so, even tho 4/5 T 9.5 bonus is OP AF, it loses its value.
T 9.5 is superior when u have to constantly AoE DPS duo to 15sec CD on DnD.

Damn, i feel bad for the 9.5 wandering plague is such a good talent with such capabilities... well back to frost i guess..

If you really want you can try t9 without disease glyph, more wandering plague procs. For fun.