Compatibility is 100%, and your particular machine is a decent architecture (not a lower-end machine to begin with).
You will notice real-world improvements with a G3/G4 upgrade that will make your users happy. The bottlenecks after such an upgrade are usually RAM (which you have enough of), video (which you may want to upgrade) and drive speed (also a potential upgrade).
I have an 8500 (originally a 180mHz 604e) that is upgraded with a G3/400 mHz and a 7600 (originally a 200mHz 604e) upgraded to a 450mHz G3. Both machines have enough RAM and perform very well. I can even coax a decent OSX performance from them (its NOT supported by Apple
Personally, I don't know how great the G4 will improve your performance over a G3. Quark won't use the altivec, and I'm of the thought it really doesn't make sense in the upgrade market much, because the architecture is already a bit slower than a real G3/G4 machine. Slower RAM access and slower bus speeds. I think you'll get the greatest bang for your buck from a G3 upgrade (as fast as you can get).
But, for most users the speed of the videocard can make a noticeable 'feel slow' sort of experience if they have a high resolution set for their screen size and the card isn't fast enough to display to quickly. This will often show itself when redrawing large portions of the display (like when moving a window) and the screen refreshes slowly by drawing the window from top-to-bottom. I've noticed it most often with a video card that doesn't have its proper drivers loaded and its simply running with some generic settings. Once loading the proper drivers the display runs much smoother (in my case I was using an iXMicro128 that was night/day difference just by using their drivers).
If you notice a slow screen scrolling or refreshing of the graphics on-screen, by upgrading to a faster PCI video card you can have faster scrolling of windows and display. For your use in Quark, the scrolling will be the most noticeable, for others when in photoshop or illustrator it would be more noticeable in all screen movement and refreshing (and I'm not talking the screen frequency refresh rate, just a visual speed of being able to move the data from the card to the display not how quickly the actual monitor is displaying it).
The hard drive upgrades are by replacing the standard SCSI drives from your 9500/9600s with a fast/wide or ultra scsi card and getting faster speed drives 7200RPM or 10,000RPM drives. If you get two drives like that and use a striped-RAID formatting on them, that helps TREMENDOUSLY with disk access times. This type of upgrade will help photoshop users the most, and if you are in a lower memory situation where you are paging information to the hard drive. But simply getting a fast drive with a new faster version of SCSI will help tremendously.
Good luck. Vive la Macintosh!
Oh, one last thing... the 9500/9600s should have the same upgrade type cards. DONT just buy a ZIF upgrade or a PCI upgrade. You need a specific upgrade for your machine. the 7600/8500s I have use the same upgrade cards (and I assume your two types would use the same as they are of the same vintage and class machine). It all depends on the motherboard types.
Normally the ZIF upgrades were for the beige G3s that had a socket and the processor just dropped into the socket in much the same way PC processors would be upgraded. If you got an upgrade ZIF card for your model (there are a few vendors you can get these cards from), it would replace your current processor card and NOT be in a PCI slot. If you go to the site: www.macgurus.com
they have a ton of information about processor upgrades and are very helpful and friendly with every order I have had from them.
Here's a direct link
to their suggestions for upgrade cards.
I wouldn't bother with a ZIF card upgrade for your machines, just get the upgrade card with the processor soldered to the upgrade card which is probably a bit cheaper and don't worry about the ability to put faster processors in at a later date. In real world sense,a single upgrade makes sense, but after that you simply won't get the performance benefit unless you get a new machine (that's my opinion). And just get the G3 upgrades, I don't think you'll see the performance value from the G4s.
[ 09-02-2001: Message edited by: bluedog ]