If you want a 17 inch monitor, get the 19 inch. CPU Prices of CPUs increase with chip speed but not linearly. Prices will be relatively level then will increase enormously with the latest offerings. For most applications, you have to double processor speed to notice the difference. The exceptions, of course are full screen 3d games and CPU intensive tasks such as photo editing.
Memory Put the extra money into more memory or faster memory.
Look at CAS settings. Check Mushkin, Siemens, and Micron to start. If you have more than one computer, network them. It can be difficult but doesn't have to be. If you can run wires, use CAT5 cable.