$60-70 is not cheap, it's overkill.
- Your speakers are by far the largest limitation to good sound with any modest sound card, including something you could pick up for about $8 at a surplus parts 'site. All you really need is to get away from onboard sound, and avoid the crude and barren cheap modern cards. $10 for a new generation card < $8 for many older generation cards.
An old $8 card with good speakers will sound far better than the cards linked here with average speakers.
- Forget gaming FPS increases, that is for EAX and related environmental audio processing with more than two speakers. Even if it weren't, the extra $ spent could easily allow you to upgrade a little more next time, offsetting the hypothetical gain because frankly, the video card is usually the bottleneck to playable framerates, not the CPU. Yes you will see some benchmark where one is higher but not much unless the framerate was so high that it was playable either way.
- Do not assume more $ equals better sound in general. Creative Labs doesn't even sell good sounding audio cards under their Creative Labs label which is for low end and gaming cards. That's why they have another label to specifically differentiate them. Their CL cards mutilate sound then they lie about digitally manipulating it so it supposedly sounds more like it was supposed to (before the card mutilated it, which is kinda ironic). All a sound card is supposed to do is accurately pass a digital stream or convert to analog, requiring a fairly good DAC (if you had better speakers, or headamp+cans so you could distinguish the difference).
The crackling popping is because Creative mistakenly assumes their card should have more bus time, as if you wouldn't have a well endowed PC but then splurge on this one card to put in a bare system. A driver can conceivably fix it, or PCI latency changes can too (sometimes), but it's not limited to nForce4 nor present on all nForce4 systems. It's present when the maldesigned Creative product needs more than it's share of the bus and the system wasn't gutted to give it more than it's share.
This is a recurring problem with Creative products, a design philosophy problem really, not just one card or a certain driver.