I understand that replacing final drive from 4.1 to 4.3, 4.47, etc Increases acceleration speed eg 0-60 in less time. (And you need a yellowbox to correct speedo.)
Q. is this at the expense of less maximum top end speed and higher revs cruising at say 100?

Q. Also if I replace my stock 16/50/225 rear tires with 16/45/225 tires the circumference is smaller, what does this do to actual acceleration top end speed. is my 0-60 faster or slower? (Igonore speedo readings).

 

your 0-60 wll be slightly faster. same idea as final drives.

 

And yes, your maximum potential top speed will be lower. But a near stock s2k tops out at ~150mph due to drag. A 4.57 rear on an ap1 lowers the max potential top speed from 166mph to 150mph...so it's not really a problem.