I think I received the same C3 as you. I was pleasantly surprised by the warm tint 8), so much so that I modded a Mini Maglite with it using Match’s mod.
Anyway, P4 and Q5 are Cree’s nomenclature for ouput bins their emitters fall under. Aside from the extra-yellow colored phosphor, both emitters should look identical because they’re both XR-E LEDs. I think the eBay P4 one may use the EZ1000 die and the other an EZ900, which is a little smaller.
seems as though the ultrafire c3's were really troublesome lights and there's tons of blf members who had problems with the aluminum versions and much better luck with the stainless steel ones ..
I don't like the light they never seemed very bright compared to other similar lights
i'm surprised you bought another C3 if you had problems with the first one ...must have been a super deal :P