Few problems with your P4 system. First, you will have problem upgrading your system later on as whatever socket it is on is gonna be replaced very soon. Second, the amount of memory is too low, I don't know what the rating of those gateway RDRAM are but if it is not 800, it suck even worst than SDRAM in most application. Heck even Intel's benchmark had their 815 chipset with SDRAM beating i820 chipset with RDRAM. Not to mention that you are gonna have less ram than you had before.
Since you don't have to spend a dime and it is obvious that whoever is buying the system for you is loaded, you should get one of those dual system P3 with all scsi stuff, and raid your HDD, at least you can load yourself with memeroy in your system, that will definately give you more performance. But hey, if you wanna brag to people who don't know jack about computer, go ahead with your P4 system.
BTW, do everyone a favor, stay away from Rambus, they are evil!!