It's really NOT the extra RAM being your solution. Not that it isn't going to happen and ultimately be useful, even necessary.
Like any machine that requires operator skills, it is that Archicad lets you make an impossible situation by putting up bad textures and asking the rendering engine to solve it with antialiasing.
With all due respect, people making renderings often cause themselves grief by making renderings that are too fine - too many pixels. It is a viscious circle, mainly caused by oversizing texture maps in the rendering. You feel that the rendering lacks sharpness and definition, so you create more pixels. And the rendering takes longer, and it still looks blurry. So you make the rendering even larger, and now the textures fail and your elements reveal themselves as crude blocks rather than finely edged architecture.
The scenario is that Graphisoft gave us small textures to minimise RAM use when creating images. When you try to make a large rendering, the textures get smeary - videoed. Chromatic abberations and blurriness happen when the antialising function is employed on an undersized texture.
My suggestions to rendering success are:
1: make smaller renderings and use a Photoshop trick called "Sharpening." This make edges have more contrast and imples way more detail in an image than that created by making additional pixels. Quicker, too.
2: Study the aspect of your presentation. How close will viewers approach? For instance, billboards, the largest imags we make, are very small files (20DPI or less) because they resolve a block away, not at arms length. We often make images with top resolution for distant viewing and this makes them less visible at that distance. Smaller file - better resolution at a distance, quicker, too.
3: A rendering shouldn't exceed the resolution of what I call its "completion level." A high resolution rendering of a crudely-modelled structure makes it look like a cartoon. Many forum members successfully use sketch techniques to disguise this, but I prefer to add visual noise in Photoshop. It softens edges, disguising crudeness, while maintaining the luminosity and shadows of a photo-rendering. Very real, but remains tentative.
4: Make better, larger textures for your texture library.Use TIFF, not JPEG. JPEG tends to have little crumby artifacts along edges that show up when they reach their size limit.Textures antialiased in Photoshop will look richer than those antialiased in Archicad. Uses more RAM in the rendering, but is faster than asking for antialising calculations.
5: Understand the context limit. Most renderings are made in a context photo. This photo needs to be highly resolved and taken from a tripod for maximum sharpness. So many high-resolution renderings are made against blurry backgrounds. Don't waste your time making a rendering that exceeds the resolution or sharpness of the background.
Dwight Atkinson