Although the nForce2 Ultra 400 and KT880 both feature dual-channel memory controllers, the different memory controllers won't necessarily offer the same amount of real-world bandwidth.
In fact, the KT880 actually offers more memory bandwidth than the nForce2 in the Sandra and Cachemem bandwidth tests.
Interestingly enough, the KT880 actually comes out behind the nForce2 at the end of the Linpack test, where memory bandwidth is the limiting factor with larger matrices. The performance of the two chipsets is still quite close, though.
In Cachemem's memory latency test, the results are far from close. Here, the KT880's memory access latency is nearly 20% lower than the nForce2.