((^Or just listen to Mak^))
oh, Macbook, OK
Macs do have good hardware. Only the software is a little iffy if you don't know OSX. If you are not familiar with it, you can always run a virtual machine of Windows on top of OSX. Look at VirtualBox. Macs were always overpriced. You pay a premium for their software.
I'm not sure if those can take up to 8GB. But what you are using it for, would not be overkill, CAD needs that extra burst. The i5 and i7 are well matched. IIRC, the i7 has Quad cores, i5 has Duos. (don't quote me on that though)