Think about it though. The fastest CPUs + a decent mobo + ram = well over $300. With a video card you get the GPU, ram, and the "motherboard" of the video card. A $300 video board is worth the money if you are into advanced visual display, whether it be intense gaming graphics or graphical development. A powerful video chip GPU can also take large burdens off of the CPU. It all depends on perspecitve though. If all a user does is minimal gaming, word processing, and web browsing, then a sub-$100 video board would more than suffice.
If you can get a retail from Dell for $100 less, I don't think $300 is worth spending on the 8500. Let's try to justify the price anyhow over let's say an OEM 8500 which is also $100 less than a retail board from BB. The retail comes stock speed @ 275/275, the OEM is 250/250. However, simple software tweeks can change this, for the OEM board is the same piece of hardware as the retail. The retail board comes with the DVI to VGA adapter to allow for dual VGA monitor support. I assume that with the OEM you need to pick up an adapter for dual VGA monitor support. Last I can think of is that the retail box comes with the three Halflife games with Truform, now could the three games be worth $100? Depending on how good the games look with Truform and also depending upon user perspective, the games could be worth about $100, which would justify retail price. I personally wouldn't care too much for the games.
I am also considering to cancel my Dell order, but I will most likely end up ordering an OEM 8500 or perhaps Gainward's $239 GeForce3 off of newegg, not another retail 8500 (unless another good deal comes up really soon)...