If you are looking at a system to do manual trading with interactive workstation style you might look at i7 or better... These would be desktop or desk side type systems with multi monitors, keyboard, mouse.
If you are looking for a automated trading system server style you would look at the zeon based systems or better. These would be rack and roll redundant back room type systems.
Of course you can blur the lines between the two...
You can do better than dell, learn something new and build your own 8^)
Cordially,
-DD-