I'm definitely moving to SSD, already have 2 X 500GB external HDD's for storage.
Should I upgrade the CPU Next ?
The lowest WEI score is in graphics but I don't do much graphics - intense gaming at all, and when it slows down most is when I'm doing Finite Element Analysis or Computational Fluid Dunamics Analysis in CAD (basically just shitloads of maths there's not much graphics at all in them) so that would make me think I should be upgrading the CPU next ?
My MoBo is A1796418A, which apparently has a G1 socket for the i7 Q740M, does that limit my CPU choice enough to warrant a MoBo upgrade ?
You can't upgrade the gpu and a cpu within the same power limits is not going make much difference. Upgrading the mobo is also most likely not possible. When it slows down, how much ram is being used? You might also want to check cpu usage too.
Everything does not benefit from more memory simply because if you aren't using it then what is more going to do.
That is only for mac, although there are products like that for windows, it is much weaker than integrated graphics. Although it's not exactly a gpu, that is a video converter/encoder (425m would be faster). There are other usb video devices such as tv tuners, capture cards, and adapters for more monitors. But usb 2.0 is limited to 2.5w and 30MB/s so are pretty weak, just enough for a video output at 1080p. I won't go into egpus since his work is cpu heavy not gpu heavy.