Yes and no. Typically, pixel frequency refers to the maximum bandwidth of the monitor, which is calculated based on a few factors, mainly resolution and refresh rate. I believe 1600X1200 @85 Hz (or perhaps its 1920X1200 @ 85Hz) requires a pixel frequency of 230 MHz or more. It could be higher or lower, I'm just going based on memory.
But to answer your question, no, pixel frequency does not have to do with the "quality" of the displayed picture, its merely an indicator of how high a resolution and refresh rate the monitor can be run at. As long as the monitor you are looking at runs a high enough resolution for you with a high enough refresh rate, then a lower pixel frequency should be fine. I believe a monitor with around a 130MHz pixel frequency runs 1024X768 @ 75 Hz and 1280X1024 @ 60Hz or so.
So, ignore the monitor's pixel frequency and compare based on the highest refresh rate and resolution; if they are high enough for what you want to run it at then it should be fine.