You may find it hard to believe- i found it hard to believe too.
But if you check the speed recordings for that series in RSA, you'd find that Srinath consistently outclocked Donald.....according to Eddie whatzizname( he is a speed fantic and keeps track of bowling speeds from as far back as he can but primarily through the 90s to current) Srinath outpaced Donald in 92 or 91 series as well...Srinath was very very quick in his younger years and through the mid 90s.....unfortunately he lacked control.... then he tore his rotor cuff and immediately dropped around 10mph on the speed guns but developed a better control....unless you've been watching cricket from pre 97/98, this is the Srinath you remember.
Donald was fast, but not super fast...whenever he's been clocked, he was in the 90-93 range most of the time.......that is fast......but not the 95mph+ stuff you saw Waqar, Marshall,Lillee,Thommo,Holding,Imran,Akhtar,Lee etc. bowling.