If you compare benchmark results from the 955X and nForce4 Intel Edition chipsets, you'll see a slight advantage goes to Nvidia. Especially in gaming benchmarks the nForce4 IE sets itself apart from the 955X. That said, it's important to understand that in day-to-day use, these differences will be small if they're even noticeable.
Even when it comes to add-ons and extras, Nvidia's unique features place it squarely in the PC enthusiast's corner. The 955X, on the other hand, takes its rightful place among multiple business segments thanks to its flexible RAID support and stronger RAID performance, as well as its AMT capabilities. Nvidia distinguishes itself from the 955X thanks to its SLI support, an integrated network controller with firewall capabilities and slightly better overall performance; it's also had a bit more time to establish itself in the marketplace. Against these strengths, Intel offers a more flexible storage controller, a higher number of PCI-Express lines and Active Management Technology. At the end of the day, the noticeably cheaper 945 chipset may prove attractive since it translates into a lower motherboard price.
By comparison with the 925XE, the newer chipsets' support for the faster DDR2-533 and DDR2-667 memory confers only slight advantages, even when memory timings are cut to the bone. The 955X is only worthwhile right now for those who sign up for the whole top-of-the-line PC performance enchilada: dual-core CPU, a super-fast graphics card and eventually even a RAID configuration. For the majority of users the 945P is only the poorer choice on paper, not in reality.