Some differences between MP´s and XP´s and P4s and Xeons are still there, though. All Xeons ship with HT-enabled circuitry, for example.
I´d say that Intel is a much better choice for dual-cpu systems right now. Several reasons exist: the AMD760MP chipset is inefficient and it´s the only chipset available for MPs. The 7505, on the other hand, is a rather robust alternative for Intel. The MPs only go as high as 2600, while the Xeons go up to 3.06Ghz - the consequence is that the Xeons that are not state-of-the-art (i.e, not the 3.06Ghz) are cheaper, and therefore, Intel-based dual-cpu systems equivalent in performance to AMD-based dual-cpu systems shouldn´t be more expensive. So I´d go Intel 2x2.8Ghz on 7505 over AMD 2x2600 MPs on AMD760MP anytime, even if that means paying a little extra.
If you look at the HT-enabled P4 (the 3.06) and see the benefit you get vs the normal 3.06 in certain tasks, you can correlate how much it would help the 2.8 duals (rought guess) and the MP's are the exact same architecture as the XP's.
"We are Microsoft, resistance is futile." - Bill Gates, 2015.