Hi:
IMO, if you have the Pentium 4 530 3 GHz and you move to the Pentium 4 650 3.4 GHz you should see a decent improvement due to the 400 MHz increase in processor speed and double the L2 cache size.
Heat will increase and you need to be real good at laying down that thermal paste.
After I made the switch, my PC's fan always spun up when the processor was placed under load.
That did not happen prior to the upgrade.
That is the only heatsink you can use and it seems to be a good one based on the design.
I probably did a lousy job cleaning the heat sink/processor heat speader surfaces or did a lousy job with the thermal paste or both!
But the PC was more responsive after I upgraded the processor.
With the P4 650, you can also run a 64 bit operating system.
I had 4 GB of PC 3200 memory in my dc7100, so I had it running pretty good.