Not only worry about the refresh time. Well a slow refresh may even not be that bad at all! It only adds ghosting, which many old CRT's had with their bad phosphors. The real thing to worry about is input lag. And unfortunately, this aspect is never advertised. To compensate for ghosting, LCD's calculate overdrive behaviour from 2 previous frames. Which means a lag of 2/60's of a second, or around 30ms. You can try this by hooking up both your considered LCD and a CRT in dual head mirror setup to your PC. Then run this:
http://tft.vanity.dk/inputlag.htmlMake a picture of both screens side by side and calculate the lag based on the difference on both screens
Although I think my LCD screen has a lag of 2 frames as well, I do not find it annoying with Mame.
About 20 inch. There is also 21.3 inch 4:3. And these screens are all awesome. Check a Samsung 214T someday. You'll love it.