🚀 go-pugleaf

Using a PCI based card will help as far as CPU utilization goes.  I read
somewhere on Intel's developer site not all that long ago that running a PCI
motherboard without any ISA cards can raise system performance by 30-40%.
The ISA bus is incredibly slow, in addition to the fact that the "hole" is
only 16 bits wide.  If you have the free PCI slot, go with a PCI card.

Also, about keeping your old SB in your machine after getting any type of
a3d card (it sounds like you are talking about the Monster Sound M80):

This is only to maintain compatibility with older DOS games.  Windows 95
games will work just fine (in face quite better) with your a3d card.  If you
do not use any DOS based application requiring sound, you can safely remove
your SB.

On another note, if your SB is the only ISA card in your system, expect to
see a general increase in system performance (not number cruching increase,
but better system wide transfers, as the ISA bus can be completely ignored.)