very cool. simple and minimalistic as logo should be. ( except the last one that's not a logo anymore
but first 3- very nice
thing you can try - try to make it consistent - weight of lines differs. letter T and O are much bigger on the top then the rest of them, try to make this right.
also consider moving letter I a little to the right, its a little of the grid if you compere it to the the right side of letter O ( this may have impact on the negative space triangles but if that the case you can work it out)
the sharp point of the top right corner letter X could start a little later so it will match the border of letter C
except that? great job