Mac Book Air struggles with external monitor

My first generation MBA is having a hard time driving my Dell 2005FPW at 1680 x 1050 @60Hz. For general purpose use, i.e., web browsing, it would be sufficient. But for extended use and coding, I’m not seeing as crisp an output as I would like.

I do have to admit, a green on black iTerm is crisp, but black on white, like in Thunderbird or a web entry form, causes me eye strain.