Norte if u weld a plate into the original rail u change just drill through and bolt your seats to em so u still have the slider and everything I've had 3 sets of seats in my ep now and only every used the original rails then they just bolt straight I'm and away u go don't see the point in spending big money on rails IMO when u can just do something simple like that
^^^^ same as above really but handling wise depends how far u wanna take it front and rear anti roll bar , panhard rod , front rear strut braces,c-pilla bar , floor bar lol this list can go on and on for handling mate
Quarter miles consist of a few things not just how much power u have got , it's about your launch your gear changes etc but I would expect it to be anywhere between the 15-16 sec mark roughly in my experience