Discussion of hardware related issues
Yes, the Exx40 changed everything just about. Added support for a LOT of stuff the prior hardware didn't support, and it was also the first version that was made in an ultrabook format (E7240/E7440). Supported dual drives in the larger laptops (E6440/E7440/E6540) due to adding support for native MSATA drives in addition to the 2.5" drive. Just was a quantum leap in terms of what they supported. And in the E7x40's, also a HUGE leap in terms of how thin and light you could have your latitude.
Also the Exx40 has the distinction for having my all-time least favorite Dell laptop ever. The Latitude E5440. I despise these laptops. Find them utterly worthless. Ugly, heavy despite being fairly slim. Only a 720 LCD offered. Despite the heft, feels cheap. We had a bunch of these at work for a few years, I hated every time someone needed help with one, I just wanted to snap the thing in half to force us to buy a new one.
Back on my Dell 7010 SFFs mainly as I just installed Win10 mainly for my wife but decided since Im supporting her and some others Id better have an install as well. Also installing on two of my laptops.
Here on the 3500 again. I've gotten so used to 13.3" laptops that this thing is just HUGE. I do kinda like it. I wish it had a IPS panel instead of TN every time I use it, but other than that I really like it for a 15". Been working fantastic with it's new SSD. Gets much better than anticipated battery life, although I think I had failed to realize that TN pantels upside is they use much less power than an IPS, so I guess there IS an advantage to a TN panel (aside from being dirt cheap). I'd still be willing to deal with the downsides of the IPS though.