A comparison of post IC temperature does not take into account the temperature of the air entering the inter cooler. Without an accurate measurement of the high temperature, your ambient to intercooled comparison is useless for comparing the efficiency of the two intercoolers.
You have no idea of the true Delta-T, the mass flow, or the pressure drop. Nor do you have any idea about the sustainability of that cooling over time. You also dont know the amount of air flowing over the core externally.
True you will know the final temperture, and that is important, but it is far from the whole story.
The T1 endtanks look perfectly acceptable to me. Only the slightest changes could be made, and the difference would be incredibly minimal. End tanks, unless they are completely retarded have a very minimal effect on the cooling.