If you can show him your work now, (slow file load times, rendering, drawing, etc.) and then say something like, "these problems can be smoothed out and sped up to
real time, so that I can get a file created and modified in
real time, instead of waiting for X to load, or render," then IMHO it will have a larger impact.
If you can point out during the demo that, say, the chopping while you spin the object is GPU based, and a better than standard GPU will stop this from happening. If a file is taking a long time to open or close then maybe the HardDrive is to blame or the CPU might be too slow. Giving him hard examples of the problems you get while using what he would see as a fine machine, would be very powerful.
Just blabbing on about hardware specs isn't going to influence him much since he seems rather inept concerning computers, but he is probably a very bottom line kind of person. How is the expense going to make him money!?
If you show him practical, real life examples of how your current hardware is inhibiting your work by sitting him down and showing him, then I think your argument would be a lot more persuasive.
Then again, if you aren?t getting slow load times or having lags in rendering and drawing, then perhaps he is the one with the stronger point. It is nice to have good hardware, but from a business perspective, it isn't always the most cost effective thing.
If he wants to get into hardware specs, look at bandwidth numbers and compare them both for CPU and GPU since that is what influences most of your CAD performance. A fast HD is important for loading those huge files, and to argue motherboard and PSU, dependability is key.
I may have missed the point entirely, but GL
PS - I still say just get a Dell Precision

There is a reason why they give them hardware different than Dimensions.
(Huge edit for clarity)