The rise time of a CW signal is what controls the band width of the signal. A good time is around 7ms. IthHas nothing to do with keying the amplifier.. Some modern rigs are so bad you can't run them next to other rigs during field day or a contest because of clicks, and garbage they generate. Just tune off frequency with a wide filter on some stations and you can hear how bad some 5,000 dollar radio's are.. my old DX60B sounds better...
Mark Amos W8XR has about the best description I have ever read.. it is posted on Tom's website (W8JI) http://www.w8ji.com/cw_bandwidth_described.htm
Just curious what rig allows you to change it (good for them). About the only manufacturer that really cares about CW quality is TenTec... my rig of choice..