Seriously I think there are basic things to consider about the use of D/S.  cpu, ram, cooling, software.

•    Now, you can get quad cord processors for a reasonable price.  There are others much larger but I don't think you really need them.
• RAM is indeed limited for use by programs on a 32 bit system.  A 64 bit system is unlimited(?) for ram.  However, when rendering it seems like speed is affected by ram.  The difficulty with 64 bit is that lots of programs out there don't use 64.  I have 4 gigs and many people say  8.
• Cooling:  this can be a big deal in my mind.  The performance of your cpu and system will drop as the heat goes up and crashes if too high.
• Software use:  When rendering in D/S if you use open gl, or hardware assist, you will not get a true view of the of the render, but it is faster.  Some people use it as a previewer then use 3Delight (full software) for final render.  My renders aren't so complex so I use 3Delight all the time.Also in the render options, under advanced you will see pixel filter selection.  These are for render image interpolation, or how the computer will see the data and convert it to a render.  I know other methods, but haven't checked these.
• Also, note that your use of many lights will greatly affect your render time.

Don't Look Back!  

 Something might be gaining on you.  -Satchel Paige