Don't have mini3, but I can tell you that T4 is about on par with a very well built cmoy with a good opamp (i am thinking of a cmoyBB with AD8066 here). However, you assumed wrongly - T3 / T3D come a year after T4, so they actually sound better than T4.
Agreed, the T3 is more open and transparent sounding than the T4, while the T4 sounds a little darker and less detailed. (haven't heard a T3D, but Jamato8 thinks the T3D is worse than the T3)
I did a quick comparison on T3 vs. T3D when I was trying to decide which to buy, and I can't really say I notice a lot of difference (at least not night and day). Though I wasn't using a particularly revealing nor hard-to-drive IEM that day. At the end the digital volume on T3D wins me over.
I can't recall what is was that Jamato8 thought made the T3D worse than the T3.