What you heard about Socket 478 was wrong. Socket 478 had no performance differences from Socket 423. What your probably thinking of was the 845 chipset, which used SDRAM. But Socket 478 boards were also available with the i850 Rambus chipset. So it's not the socket, it's the chipset, and there are good boards with the i850 chipset in Socket 478.
But none of that excuses the lackluster performance of the P4. The reason for getting a Socket 478 motherboard is for future upgrades to the Northwood core P4, which will be less lackluster than the current Williamett version. And even that will most likely be a bit slow and expensive.
So that leaves you with the Athlons. The current crop of XP's are even better than the already good T-birds. AMD's biggest drawback has been their reliance on VIA chipsets, but now you have several chipsets to choose from: SiS 735, 745, ALi MAGiK 1 (now in revision "C" for improved performance), and the nForce. While the nForce and 745 are new to the market, the 735 and MAGiK 1 have prooven themselves stable enough for use under Windows 98SE.
What's the frequency, Kenneth?