Nothing wrong with AGP4x.
Ive got a beefy R9700pro running on 4x fine.
At the moment agp 8x is pretty much a marketing gimmic, like ATA133. very minimal performance benefits except in select applications.
the 4800 is ok, but its the same as the 4600.
See if you can find any cheap 4200, 4400 or 4600's around.
No other precautions really, except if your cpu/mem subsystem is relly feeble (<1000Mhz) you may not get all the performance you expect.
<b><i>"Why don't you try practicing random acts of intelligence and senseless acts of self-control?"</b></i> 😱