I'm not sure if I completely understand the question either... If you're looking at monitors and one claims XGA and another claims SXGA, there may still be other difference. Between manufacturers and models, brightness, contrast, switching speed, pixel size, viewing angle, power consumption, etc, may vary considerably. A high-quality XGA display may very well be better than a cheap SXGA. It's best to take a look in person and see which ones you think are best.
Pentium IV 2.4C Northwood- M0 stepping @ 3.2GHz HT
Air Cooled w/ SP-94 heatpipe & 92mm Vantex Tornado at 45C
4x256=1gb dual-channel 2-3-3-6 OCZ PC800DRAM @ 890MHz 3-4-4-8
MSI Neo2-PLS w/I865PE & SATA @ 4x267=1068MHz
BFG GeForceFX 5900@485/967MHz = 6284 3DMark2003s; dual-head 21" CRT & 19" LCD