The chronology I remember is a bit different (GNOME needed a replacement for CORBA and came up with DBUS; KDE already had DCOP; then Freedesktop happened, with big players pushing to reduce mismatches so that they could ship both environments with less hassle; and KDE scored some and GNOME scored some (more), with DBUS being one of them), but I was just a random observer so I might have got it wrong.

Still, it's a fact that DCOP back then felt much nicer and more humane (I wouldn't know about speed). I haven't used Linux in a while so I honestly don't know now.