Front suspension arm kit help for s4

hmm i was actually looking at this/thinking about this just yestarday...

I've noticed that the A4 kits usually say doesnt fit S4, but seen as they have the same track, and S4 uprights fit A4's just fine, what exactly is the difference between the two kits?
 
i thought s4 was the same as a4 just rs4 was different.i have an ebay kit on my a4 and it seems fine.
 
found this om ecs tuning web site "the difference between a A4 & S4 is the style of tie rod end & the upper control arm bushings. The two kits are completely interchangable fitment wise"

on ecs site the s4 kit is loads more than expensive than the a4 kit,
are the s4 more durable with the heaver loading / wider tyres? or is the handling/ feel better - these are just my guesses
.....anyone know the real reason for the difference and is it worth it?
 
I believe the S4 parts are aluminium and the A4 steel, I could be wrong though
 
Both A4 and S4 upper arms are aluminium.

Only difference is the rubber compound used in both.

Harder in the S4, otherwise no difference.
 
i would imagine that new A4 arms are still going to be better than old knackered S4 ones even if the original S4 ones were a bit stiffer. You could always swap the top bushes (or all of them) out for poly ones.