[underscore]

here's what I see:

1) since your boss is just getting you to pick out the parts, it's doubtful he'll notice small differences in performance, especially when he's not directly comparing to the other option. so finicky little bits like the slight difference in RAM speed don't matter much. From what I gather SkinnyPupp puts together machines all the time so he's seeing them side by side to compare.

2) Since this is a business machine, have you given consideration to backup media? I don't know your exact situation but if the HDD shits the bed and loses a bunch of company files, that's usually bad.

3) Related to 2, is that if you buy a prebuilt Dell machine as a business, you're also getting the business level support. From what I am told (forgive me if I am wrong) they give damn good support to businesses should something fail, whereas if you build it all yourself you're dealing with individual manufacturers as a regular user. The importance of all that boils down to how important it is that this computer stays running as much as possible.