Welcome to the forum.
The G series is a little more up scale than the S# IS series...but they are different. The S series has twice as much zoom but the quality of the lens, especially at the long end, will be compromised.
I believe the G9 will record in RAW format, which is important for serious digital photographers but maybe not for everyone. I think the G series has a hot shoe, I'm not sure about the S series.
Really, in my opinion...I'd skip the digi-cams and go with a DSLR...but that might not be practical for a 'family' camera...and it blows the budget.
I guess the best thing would be to carefully weigh the features and then make sure you hold them both, and see which one feels good and meets your needs. They are both very good, for digi cams anyway
As for faster cards...they allow the camera to clear it's buffer faster...so if you are shooting many, many photos in rapid sequence...a faster card may allow you to shoot for longer. I'm not sure what the affects are when using these cameras in video mode. Also, they download faster. But in day to day, average shooting...they probably don't make much difference at all. Although, a slower card may take longer to bring up the image on the screen when viewing...but if you didn't have a faster card to compare it to...you probably won't notice. So buy faster if the cost isn't much. I wouldn't spend a whole lot more on it though.