Yes, the card itself is great, AGP did die before it's time, it's only dual GPU and the very top end cards that need more than 8 lanes even today, they wouldn't throttle back PCI-E slots to 8x if the cards didn't work, but of course, AGP didn't provide the same level of power either (and I’m sure there's something about latency as well). My Card is also a Sapphire, just the 3650 512MB. I had considered a while back of getting the 3850, but since I’m CPU bound, it would have made almost no difference for a 40-50% price premium.
In terms of the overall system, P4's really do show their age now - despite their popularity. Mine is a Socket 478 Prescott 90nm with Hyperthreading with a default clock of 2.8Ghz, OC'd to 3.1. Back in the day, it was running 3.4Ghz, but age does strange things. The CPU could hit over 3.6, I know it could, the problem was memory, I had generic Crucial 512 DDR400 modules and they couldn't overclock at all. I had to do some very heavy memory ratio's since they were locked to the FSB, and it was through the FSB I had to do all my overclocking, made things a lot simpler compared today. Even with the timing's at their highest of 2-4-2-8, they could never past 411Mhz. so with a CPU at 3.6 and the memory at 340Mhz due to the ratio (can't remember the exact values), my performance was worse than if I kept the CPU at 3.3 - 3.4Ghz. All this was done on Air cooling using a Thermaltake copper Tower cooler and 2x high speed 'Streetfighter' fans... the noise can get pretty damn bad, not Delta levels, but still bad.
The other thing as well is 2GB of ram really isn't enough anymore, for me at least, I have 2GB and I keep hitting memory based walls in applications (rendering and Graphics packages like Photoshop and Illustrator). I run WinXP so that I can keep as much memory as possible, though I will admit it's only been in the last year have I actually started to really need more than 2GB and a 64bit OS. I can put a fair bit of blame on Firefox, it is a real memory hog - I use 3 windows and about 30-40 tabs (yes, they're all used) and the memory footprint is about 300MB+ and virtual memory at about 400MB, I believe the 2 culprits are the javascript engine and flash, but we'll see when FF 4.0 gets released with the new javascript engine. But when I start throwing Mail clients, RSS readers, Office and messengers into the mix, I have about 400MB left - which can promptly be snapped up by Firefox.
Yes, I might be a bit of an extreme case but all I’m saying is, if your going for a new build, go 64-bit with 4, 6 or 8GB of ram, at least then you'll have some spare as you continue to use the system for a couple years.