http://www.tcpglobal.com/itemdetail.aspx?itemno=FIB+400I use that, but they have several grades. Evercoat also makes my favorite Rage Gold body filler, so, by using same brand chemicals there is a better chance that its made to work together?!
I am very persistent and I have no qualms about sandblasting a part and starting all over again. For me, its about doing the best job possible, so time, profit, etc isn't part of the deal. Frustration however, that is in abundance to say the very least!