Precision 5510 and Tb16 - how many monitors?

I have a precision 5510 running win 7 connected to a Tb16 dock.  I have 3 external monitors working.  Is it possible to add a 4th external or use my laptop screen?

I read in the Tb16 manual you can have a quad setup, but on dell's website it states on 3 FHD monitors.