Worst computer I have worked on.  Constant problems of all sorts, including the difficulty getting it to wake up, the heat issues and fan noise that others report, plus crashing and many more random things.  It is supposed to be a high performing CAD machine, but it gets overwhelmed with standard work of a professional.
Ill conceived user experience.  It requires two hands to pry open the lid. Why?  It can't figure out that if headphones are plugged in, it should route audio to them and turn the volume down from what the built-in speakers require. 
Dell support is poor, with no resolution on issues after many months.  I have probably lost an entire work week dealing with this 5540.

I'm using one for the business for 2 years. It's fast but not stable. Come back from lunch, have to reboot because it shut down or went to sleep and does not wake up. Or keyboard not working. Also, fans are running for nothing. Just some work and fans are running. Very annoying...

Better construction, keyboard, touchpad but much worse thermal management than in Precision 5530 model (6 core CPU in both models). Fan is too loud when kicks in.

You reported that "in battery mode, Dell's workstation only scores 673 points in the multithread CPU test." Does this mean the laptop works only at half power in battery mode?

"Workstation doubles as a Handwarmer"

Is that one for me?

But actually, I don't think its that bad. Despite my criticism of Dell, this is a big improvement over the XPS 15 which has similar processor and similarish gpu. It also runs cooler than the Lenovo P1.

While I would prefer temperatures stay at 45 or below. It's still an improvement for Dell who has some laptops with integrated graphics going into 50s.

So good job Dell at making a laptop that grandma can't use to bake cookies. A hand warmer is a big improvement.