Thanks - this is what I did
Based on the responses in this thread and other info on this forum I made two upgrades to my Mac Pro 3,1, that really made a big difference.
1) Graphical Card
I changed my ATI Radeon HD2600 card to a ATI Radeon HD5870. Bought one second hand on Ebay and it works great. Graphics are faster and the card is more quiet. What you need to know is that you need to attach both power cables to the card. At first I only attached one power cable and than the card did not give any graphics. With both power cables attached, all worked as planned.
2) SSD
I decided to install an SSD card, which I will use to boot from, run OSX on as well as all my major applications. I did buy the following:
a) Apricorn Velocity X2 - this is a PCI card that you can install in PCI slot 2 (assuming your graph card is in PCI slot 1).
b) Crucial M500 SSD memory, 480 Gb - this is the actual SSD memory, that you buy separately and install on the Velocity X2 card.
Installing the SSD card is easy - just slot it in PCI slot #2 and power up your computer. Than go the Disk Utility and Erase it, so it is ready to go.
I had some trouble installing OSX on the new SSD disc and (by memory), this is what I did (SSD card is already in and formatted):
1. Power down computer, than power on computer pushing Command-R. The computer starts in "Recovery Mode", showing a startup menu.
2. In this startup menu, you can select to install OSX. Select this option - now you can select on which Disc to install OSX - choose the new SSD Disc.
3. During the OSX installation on your new SSD Disc, there is the option to transfer information from another Mac or Disc. Select here the "Old" SYSTEM disc containing your operating system (the disc that you booted from before"
This will now take a while, but than your SSD disc is the one which will contain everything that used to be on SYSTEM. It is used to boot from and all is great!
I am not at all a computer nerd, but this is what I did and what worked.