How can I evaluate the quality of a scanner system?

The quality of a scanner system (galvo system) is not easy to determine. The scan speed is only one factor that needs to be respected: There are very huge differences between a good 50kpps and a bad 50kpps system.

A very important factor is the angle stability of the system, meaning how precise the system works if the scan angle is widened up.
If the scanner is properly centered aligned, the scanning behavior is usually Gaussian shaped - with the scan angle as variable.
Evaluation of scanner quality is quite tricky and needs some deeper knowledge of other components like the mirrors used or software settings.

In general we recommend to use either Xscan, Xscan 60, CT-6210HP/SE or CT-6215HP (whereas CT-6215HP is the best option) if you intend to do professional graphics projections.

The wider the scan angle, the trickier it is to get good scanning results. The limitation in speed results from the incredibly high frequency the little mirrors needed to be moved with.
This mechanical limitation is also the cause why it is not possible to project areas, but lines.