Psx, I wish I could tell you. I am so conflicted about this right now, it's actually pretty bizarre.

I am going to get the Duron, and overclock it. I just saw the tbird, and thought the price was good, so it tripped some sort of deal trigger in me. BAAH, see what hanging around here too long does..

I can't even look at a sale ad anymore without thinking how to pricematch it to staples and use a coupon.:Q
No, I don't think the cache will make that much difference, except for benchmarks. (As someone, Johnny maybe, said earlier). Realworld performance will be roughly the same. Yes, I do agree that the duron should overclock more easily.
As I said, I am going to buy the Duron. If I can find someone that has a good price, and a decent warranty, that'll be great, I'll go with them, as I hope to overclock, but I don't have a whole lot of time to sit and tweak everything to heck and back, so I may end up just running at stock speed. In that case, seems the Duron would be good, still.
Those are my thoughts for now...
Subject to change (but I don't THINK they will this time.)
Tiger