Duron? You're kidding? I never had one but I heard nothing but good things. Fun little fact, it's the only CPU (that I am aware of) that had a smaller L2 than L1 cache.
Duron was the budget king. The only difference with the higher end Athlon, was the reduced L2 (only 64KB, but fullspeed). But it didn't matter that much in practice because the L1 cache was huge for the time (64 + 64KB), and the L2 was unified. So in effect you had a 192KB L1 cache, with a fast and slow segment.
Yes I had two different Durons, 700MHz and 900MHz ones and they didn't even run like 700 and 900MHz CPU's, they seemed to be more like Pentium 3 366MHz. They were so sluggish in everything.
Did you by any chance run with regular SDR-133 memory? Duron really shined with DDR, preferably DDR-200MHz, so it was synced with the system bus. Especially the later 1GHz+ with the Morgan cores were beasts for the price.
Ah, those ECS K7S5A memories...