Even with your fairly weak pump you should still get close to .75 gpm through the block with (what I would suggest using) #4 plate. At that flo rate the TDX will definatly beat the Asutek block on the same setup. Peop[le seem to look at the way of getting WB and pump matchs wrong, they seem to think if one block is more restrictive than another you should use the least restrictive block with a weak pump. To me it is usually the opposite, the high restriction blocks all seem to do much better at the low flo rates.
Like the mcw6000 will get better temps at .5gpm than a maze4 will at 2.5gpm. But the 6000 seems to have about the flatest flo vs temp graph of all the major blocks. Also most any pump will get .5gpm through most any block with a decent flo system ie 3/8 or bigger tubes and a non-windingtube style rad.
Also if/when you upgrade your pump the difference will only get larger.