Max. Upgrading Leopard 10.4.11? MacBook Pro 17" A1212

The limit of your hardware will limit how much Memory or HD storage you could support. Any of the OS-X OS's could be used as their limits are much higher than what this system could support.

It should be noted having too much memory or HD storage is also not wise. In the case of portable systems you will not have the length of battery usage as well as added heat with higher storage levels and system wouldn't necessarily be faster for it as well. More memory & storage requires more indexing which can slow your system. Also as you use your system files will end up being scattered across the HD platters requiring more seek time.

At this time you could replace your current HD to a 1.0TB HD and if you still needed more storage you could replace your optical drive for a second 1.0TB drive using a special carrier. You could also use a SSD in place of the optical drive making it the first drive so you have almost an instant on system.

I would recommend getting external firewire HD's to extend the systems storage Vs putting everything inside. As an example I store my videos and music on an external so I can watch or listen on any system I have.

The memory limit is 8GB two 4GB PC2-5300 memory modules on this system.

Both hard drive and memory technology is progressing so larger storage options will likely arrive on the scene which may even use less power. So don't go to far here as you may find next years solutions will be even better.