You should know, that implementation of GPRS&EDGE can or can not affect existing capaticity. Depend of appropriate parameter settings, you can define a lot of different situations. What kind of equipment do you have?
I’m taking about SGSN Planning because it has different conections with each GPRS’s element.
Also if you want to assure some bandwith for area you must dedicated channels in air interface.
We’re using Nokia solution