ProBook or EliteBook

I have been researching a new computer to use for office work and travel (see my What Notebook Should I Buy? form here.) I took a look at some ASUS and Lenovo notebooks, but I still keep coming back to the HP business line of notebooks. I have had a Pavilion that has lasted incredibly well for 4 years now, so I am pleased with HP really.

To simplify, I'm looking to use this computer on the move for simpler office tasks, but will possibly also do some graphics design, web design, video design, or light games on the computer as well. Still, build quality is the biggest consideration here.

I'm now trying to make a decision if I could be fine just getting a ProBook, such as the 6540b with the i5-430M and Intel HD integrated graphics and add on a three year warranty coverage, or go ahead for the best and get an Elitebook 8540w/p with an i5-520M which comes standard with a three year warranty coverage.

I guess I have a few questions for your expertise and experience here.

1) Is there quite a notable build quality difference between the 6540b and the 8540w notebooks? I am aware that adding a three year warranty plan on top of the 6540b price brings it pretty close to the price of the 8540w.

2) Is there much difference in the GPU performance between the Quadro FX 880 on the 8540w and the NVS 5100 on the 8540p? This seems to be the only difference between the two models, so I was curious if the added price was worth it for me.

3) When I make a purchase I will be upgrading the RAM to either 4 GB or 6 GB of DDR3 1333 and install an OCZ Vertex or Intel SSD drive. Given the intended uses and the above questions, do you feel that it is worth it to go for the more powerful and more expensive Elitebook? Will there be a noticeable performance difference compared to the ProBook 6540b?

Thank you in advance for all of your time and help!