I have 8gb ram and a 512 SSD. The biggest speed improvement I have seen from my machine is when I moved to using referenced files with Aperture. I store the files on an external FW800 drive, the library is on the SSD.
When working in Aperture, I do sometimes have a fraction of a second lag due to the files being on the external, but Aperture works much faster, much more 'snappy' in general with this configuration.
I think the OP is asking for help on two overlapping fronts here, and no one seems to have the experience or setup to answer both of them at once. I don't have the proper setup or experience either, unfortunately, but breaking out the questions might help.
The first question is if aperture itself simply runs more efficiently and is more responsive when the library does not store the master files as part of the library, but instead the masters are stored outside of the main library and referenced by aperture. I've seen posts here arguing about whether or not it makes a noticeable difference, but generally there are some people that seem to swear Aperture is more responsive when operating on referenced files, especially when compared to managed libraries that have grown to a significant size. I don't recall seeing anyone argue that referenced files slow down Aperture, so if I was to err on one side, I'd probably err on the side of using referenced files.
The second question is if you would only see a speed up in responsiveness by using referenced files if the referenced files didn't live on the same drive as the library. I have no idea, here, so I hope someone with experience that has looked at it both ways, and preferably with a SSD, can weigh in. If I had to guess, I'd say that the speed of SSDs these days means that having the referenced files on the same SSD would still be quite snappy and responsive compared to having them on an external.
When all is said and done, I think the optimal setup would probably be something like a library living on one SSD and the referenced masters living on another, but I really doubt that that would make a noticeable difference over the single SSD reference file setup.
I moved completely to a referenced setup this weekend, with the masters temporarily located on a big USB 2 (gasp!) drive, and the libraries located on an internal SSD. I was *amazed* at how trivial of an operation Aperture made it to move the masters around through the 'relocated masters' command, and even how easy it was to reconnect the masters if I decided to rearrange the file structure outside of aperture (which I wouldn't plan to do). Given how easy it was, I would think that your workflow would benefit most by ingesting them into a managed library and working on them, then just do a 'relocate masters' when your SSD starts to fill up. You wouldn't have to do it every time you pulled photos in, just when your disk started to get full. That operation is so painless, and you don't have to sit and watch it, that it unquestionably will speed things up if you're performing the same operation on thousands of files.
As a final note, I will confess that I was quite surprised at how usable even that big slow drive over USB2 was when using the library on the SSD. It bogged down when I had it stamp a bunch of edits onto a whole series of images, but when working on individual files, it was surprisingly responsive.
