I got it fixed now (somewhat) but it should be easier than this.
Here's what I did, might not apply to you equally:
Note! I first tried #3 straight and it didn't seem to work but now I've discovered the custom resolutions is bit buggy so it might work or might not without the 1-2 step.
1. Updated to latest driver that came out recently in WU, it did not fix the issue
2. installed monitor driver - looks like during upgrade the monitor driver got uninstalled.
(2b. Actually it refused to install the monitor driver from Samsung's original inf, so what I did was find the Monitor.inf from System32\DriverStore and looked at what was the closest model available and added my resolution there just to be sure)
3. That didn't actually seem to do much of anything. So I went to the Nvidia Control panel that now appeared after driver update and into the custom resolutions. First I tried using the simple settings, just setting res,refresh and keep in Auto. Didn't fix it. So then I tried to put it into various other positions (GTF,CVT).. That seemed to finally do the trick. The DMT setting seems to be broken in Win7 as that results in the incorrect resolution.
Conclusion: The new Win7 aren't 100% identical since the same settings (Auto/DMT) couldn't be used and I hadn't backed up the old custom values so Manual was out of the question. I can see from User timings screen on the monitor that the new settings aren't exactly same and the text is a bit fuzzier still. Bleh.
So if you still have Vista there with the OK settings, create a custom resolution using the good settings as template and take up the values so you can get them right in Win7 as the Auto/DMT setting is broken.
Here's boring explanation of those:
Generalized Timing Formula (GTF) is a method of generating industry standard timings used by a wide variety of display products
Display Monitor Timings (DMT) are a list of VESA standard pre-defined timings which are commonly used within the Computer industry.
Coordinated Video Timings (CVT) were released on March 2003 as the newest VESA standard for generating display timings
Coordinated Video Timings-Reduced Blanking (CVT-RB) is geared specifically for non-CRT display devices. CVT-RB offers reduced horizontal and vertical blanking periods and allows a lower pixel clock rate and higher frame rates.
EDID Timing is the preferred timing standard defined by the display's Extended Display Identification Data (EDID) value. EDID is a standard data structure that defines the display device's configuration data and mode support which allows optimum use of the display