1st) I highly assume that DXTory wont do any special filtering, it will just resize via nearest neighbour method.
2nd) For youtube I cant recommend lanczos4 anymore. It uses too much sharpness and as a result of this, it has heavy ringing problems. Both make the material very bad compressable. For youtube it is important to have the material as compressable as possible. So try rather Spline16 and the Blockbuster Filter @ the following settings:
Blockbuster(method="blur", detail_min=75, detail_max=100, strength=100, block_size=4)