Anything will be a huge increase over what you have now. Even an A64 at 1.7GHz will be like 2.5-3x faster than your Celly, so I wouldn't worry about 200 MHz going to a 3000+. IF you're overclocking there is no difference, they will both top out about the same. Almost all the newcastles top out in the 2400-2500 range
There is ZERO difference between SATA and PATA for the same base drive. The Raptors and 15k SCSI drives are a little faster, but not enough to warrant the price difference in my opinion.
If you're playing games, your biggest problem is your video card. Period.
512MB is okay for now, though you will probably want to move up to a gig eventually. An overclocked 2800+ is enough to make even an x800XT or 6800 Ultra the primary bottleneck of the system in most games.
Check this chart from the recent P4EE review:
http://www.anandtech.com/cpuch...c.aspx?i=2261&p=13
And see that the only thing that the A64 2800+ is under 50FPS average in is the Sims2. In most games it's over 80FPS. This means that the CPU is capable of at least those framerates 60FPS in almost any game and much below that will be entirely the cause of the video card. overclock to 2400MHz and compare the 3400+ to the highest end CPUs... You're within This says that the video card is the primary bottleneck even in this case where they are using an x800XT.
Try not to get caught up in CPU MHz. At this point even the mid to bottom end CPUs are capable of delivering all the performance you could want in games. Games have become so dependent on the video card, that the CPU is actually not all that important.
So if you keep this in mind when buying a new system, you can save money on the CPU side and spend it on the video card side.