Blade: you'll hear a difference only because the all Creative cards resample all output to 48kHz, and all cards prior to the Audigy 2 ZX are notoriously bad at this resampling. Take a good sound card (or even a cheapy like the Chaintech av-710) and you won't hear a difference. The only place you'd hear a difference is on source material that has to be downsampled/converted to match the max output of the card, and this is only usually heard if a poor algorithym is used.
Mafia: Most normal humans are usually only sensitive to the upper 15khz to lower 16 kHz range. Some people can hear slightly higher. Only newborns really hear up to 20+ kHz. Hearing range decreases with age.
You can test your hearing with this sample:
http://ff123.net/samples/sweep.zip
Use this page as reference:
http://ff123.net/sweep.html
*Note* this sample can only be used if you have a sound card that does not resample (that leaves you Sound Blaster users SOL)
To all: Don't confuse Sound Pressure Level (dB) with Sensitivity/signal to noise rating. Even though they both use dB as a unit of measure, they are two totally different measurements. When refering to a sound card the dB number refers to signal to noise. The chances of actually hearing the difference between a 91dB s/n and 100dB s/n is slim. Almost all pc speaker amplifiers and/or electrical interference inside the pc will add more noise than this slight difference would make audible.
As for the SPL difference between 91dB and 100dB, you most certainly would hear it. It is nearly twice as loud. Every SPL increase of 10dB doubles the PERCIEVED loudness.
To answer blade's original questions:
1) No, the 91dB to 100dB s/n increase would be hardly noticeable, especially with pc speakers. If you were to run an unprocessed digital out to a very good amplifier (which is nearly impossible with any Creative card), it may make a negligible difference.
2) As for sampling rates, it really depends alot on the source material sample rate and whether the card itself resamples and how it handles this. Creative cards are locked to output at 48kHz (therefore, every other sample rate is converted prior to output, and they do a poor job of this). You can test this with this sample:
http://www.hydrogenaudio.org/forums/index.php?act=Attach&type=post&id=3
Read this thread:
http://www.hydrogenaudio.org/forums/index.php?showtopic=9772
*Caution*
Play udial.wav at a very low volume, it can cause speaker damage.
3) I've never heard the Inspires, but I know they are not considered nearly the best, you might hear some stuff, might not hear other.
If you are looking for a good (and cheap) soundcard (and don't need hardware EAX), one of the most recommended cards is the Chaintech AV-710 for $26 at Newegg. It is stellar at bit perfect digital out and has a wonderful 2 channel output on channels 5/6 because it uses a Wolfson DAC on these channels. The card is based around the Via Envy24-HT chip whose brother, the Envy 24, is found on many, many pro-level recording cards.
I hope I cleared things up a bit.