[whoopdedo]

I only have my unreliable memory to say, but on a 486DX/33 I recall play Doom 2 at least on the second-from-top view size without noticeable lag. But what sound card did you have? In the late 90s hardware manufacturers made budget cards with processing being done in software rather than dedicated chips. If you had one of those it may have been too much for a 486 to handle. Also probably the cause of your modem problems, as "soft modems" were notorious for being unreliable.

Obviously these cards were meant for use in Pentiums with their extra processing power. But some stingy integrators coughPackardBellcough would slap together the lowest cost components without regard to if it'd actually work properly.