You are asking the right questions in the right forum. Unfortunately for you, most of the heavy hitters are at SolidWorks World right now, so you may not get many answers till next week. I will give you my pathetic attempt at an answer, but I would wait till you hear from the truly knowledgeable.
For most of your students, a low to mid range SolidWorks approved graphics card will work just fine. People who do very large assemblies or Flow Simulation with lots of graphics say that the more expensive cards help. Most people find that the added money buys very little, if any, improvement. When my assemblies spin around without any perceptible problems, any improvement in frames per second is useless. I haven't used either the K600 or the K1100M, so I can't say anything about them. You were lucky that the Radeon cards seemed to work out well for you. It seems like the newer versions of SolidWorks demand more and more from the graphics cards, so an approved card seems to be a better and better idea. You may be able to find hacks to make a game card act like an approved card, but I would rather spend the bucks on an inexpensive approved card.
Desktops will always give you much more performance for the money spent. I would only go for laptops if portability is a requirement. Desktops are also a lot harder for someone to walk off with.
I don't have an SSD, but from the comments that those who do make, I wish I did. Since launch and load times can be pretty significant, I would want one even if it didn't make any difference when I am actually working on a part, assembly or drawing.
Most of your students are not going to need more than 8 GB. Again, it is the large assemblies that will use up RAM. SolidWorks does seem to have memory issues (but I am still running SW2010, so they may be fixed in newer versions), so having more RAM may mean longer times between weird behavior causing a need to reboot. RAM is pretty cheap.
You can read posts in this forum that discuss CPUs and I strongly suggest you do so (although I suspect you have, given the setup you chose and the questions you are asking). My own vague memory is that i7s are a little faster at the same clock speed as i5s, but I would not trust that memory. Clock speed is critical for SolidWorks. It only uses multiple cores for a few things, so more cores (or hyperthreading) doesn't usually help.
My first priority is CPU. After that is enough RAM, but any more than enough doesn't help. A low to mid range approved graphics card is next. Storage is last.
Work with Dell sales people, rather than just using the website. There are options that don't show up on the web.
I'll second what Jerry has said. As a former SolidWorks instructor, the vast majority of what the students will be learning won't require more than 8Gb RAM, and a mid-range graphics card will work just fine. I, too, would stick with a desktop unless mobility is needed.
If you're going to be purchasing a good amount of PCs, definitely talk to Dell directly.
If we have the budget, I think we will go to the high end of what we need. These of course of probably more along the lines of "Desktop Replacement" due to their weight and size, but they will do the job.
Current Specs that we are looking at: Dell M4800
AMD FirePro M5100 w/ 2GB GDDR5
16GB of RAM.
Sounds like it is overkill for what we need right now, but hopefully that means it will last a while before it will need to be replaced. I am Definitely planning on talking to our Dell rep to see if we can get a good deal on the machines.
Thank you very much for your input.