i kinda regret not getting the 680MX. I'm in the same boat. I used Aperture 3 a lot and will be delving into amateur videography soon (Just purchased a Canon G10) so it probably would have helped. Also, probably would ensure more future proofing once Aperture 4/5 come.
I am a bit inclined to transition to LR4 as Apple seems uninterested in developing Aperture beyond a point release.
Do you guys think the 660m (with 512mb of VRAM) will be enough for standard aperture 3 usage?
The fastest GPU I've used was a Intel HD Graphics 4000 on a 2012 MBAir Core i7 with SSD and NVIDIA GeForce 9600M GT on a 2011 MBPro Core i7 with HDD. These are positioned by at "211" and "242" on
notebookcheck.net's Laptop Video Graphics Cards - Benchmark List. The 660m is positioned at "56" vs the 680mx positioned at "7".
Do not worry both Kepler GPUs (680MX and 660M) are considered "High-End Graphics Cards" while half the GPUs I've been using are "Low-Midrange Graphics Cards" and the other half "Low-End Graphics Cards" I've put up and survived with it.
My images tend to be around 16-32GB of RAWs from a EOS-1D Mark IV, EOS 5D Mark II, and EOS 7D at the high end.
The benchmarklist has a complete notebook GPU listing and some desktop GPUs for the purpose of comparison.
As for going a full SSD setup... I am on the bench with that. I ordered a 1TB Fusion drive. By 2016 I may decide to break open my 2012 iMac and install the "stick" SSD and a 2.5" SSD if the capacity is more than 4TB with 600MB/s read/write for $200.
The numbers I mentioned can be a reality in 3 years time.