I've got 3 Slim systems here, a PAL 90k, a NTSC-U 79k and NTSC-J 77k, i converted all 3 to Retail-DEX NTSC-U systems, all 3 ran the same as far as i could tell, interestingly tho, every system (including the stock NTSC-U 79k) all had the slight screen tear you mentioned at the top of my PS1 game...