Dell. What processor to choose?

Hi guys.
I'm planning to buy Dell Precision 7710 laptop and now choosing the processor.
I'm working with After effects and 3ds Max so planning to choose the Graphic card Nvidia Quadro m5000m (8Gb), and 64gb RAM ECC. There are several types of processor so I'm wondering which is better for my use.

Here is the choice:
- Intel® Xeon® E3-1505M v5 (Quad Core 2.80GHz, 3.70GHz Turbo, 8MB 45W, w/Intel HD Graphics P530)
- Intel® Xeon® E3-1535M v5 (Quad Core 2.90GHz, 3.80GHz Turbo, 8MB 45W, w/Intel HD Graphics P530) [add $76.56]
- Intel® Xeon® E3-1545M v5 (Quad Core Xeon 2.90GHz, 3.80GHz Turbo, 8MB 45W, w/Iris Pro Graphics P580)
I see that there is slight difference in GHz and integrated video. But the price difference in some instances is more than $500. So my main task now is to clarify is it worth of saving this money.

So I would like to ask you guys
1) how big is the difference between 2.8GHz and 2.9GHz in performance?
2) Since I will use Nvidia Quadro m5000m does the type of integrated video card (HD P530 or Iris Pro) is still important for my use?

Thank you in advance for any help or advice.
Alex