My monitor has focus controls, horizontal and vertical. These are in the control menu but they don't seem to do much. Other than these kind of controls all monitors have a gross focus control (don't know the real name of it) but it's inside the case. I don't recommend touching this unless you know what you are doing. High voltages can KILL you!
I've adjusted this focus control, exactly twice, once on each of my previous SVGA monitors when they got old and "tired". I didn't know what I was doing but I didn't want to buy new monitors before they actually failed.
If your monitor is sharp at one resolution but not at another then the gross focus control won't fix the problem. The control affects all resolutions.
I have one more thought. Is your 8500OEM a BBA (Built By ATI) or is it an ATI partner card? The latter could possibly have bad RF filters like I described with older Geforce cards. The MOD I've performed on two Geforce cards I've also done on an old ATI All-in-Wonder (original Rage2 not Radeon) but I've never done it on a Radeon or later card and didn't think it would be needed.
It's was just a thought. I've never heard of any Radeon, Radeon 8500, etc, partnered or BBA, ever having this kind of problem with RF filters. It's just that you have the symptoms, sharp at low resolution, blurry at high resolution.
<b>99% is great, unless you are talking about system stability</b>