The A4066 may be the one exception since it was prob. one of the best old ethernet cards you could get speed wise and the only one i haven't owned. I have tested just about every other ethernet card out there with MNI drivers and with sanaII and they come up slower in Miami than Roadshow. Roadshow actually triggered a bug in the x-surf drivers that got fixed if i recall.
So what speeds do you get on the A4066 and Miami?
I have some netio and tcpspeed benchmarks saved somewhere, I'll try to dig them out. The impressive bit was that with Roadshow, the Ariadne (original model) was equal, or perhaps slightly better performing than the A4066 using MiamiDX+MNI. Measure both cards with MNI drivers and the 4066 is clearly better.
I don't recall any significant differences in the numbers between the two stacks with the A4066, but the A4066's poor SANA-II driver provides a bad overall experience, where it's seamless with Miami (especially web browsing).
Ultimately, I left the Ariadne in the machine because of the newer stack, similar performance, and the unfortunate fact that the A4066's SANA-II driver doesn't support multicast, so no Shapeshifter.

It's a shame, because with its better hardware, the A4066 could be king of the classic cards. Getting the best out of it means sticking with Miami.