Ive driven rst's with standard boxes, and with quick shift shifters, had a spin in crazycages fiesta which has the focus rs cable linkage box, it is starting to show signs of wear which I couldnt notice, the feel of it was unreal so smooth and precise with very little travel between gears. Dont know what the 170 box is like but you can take it from the focus rs box is one hell of a good mod to consider.

Hope this helps

Raj