Re chevvron's "holes", quite apart from the different MTI threshold speeds, this is an inevitable consequence of replacing raw video display radars like the Watchman with plot-extracted radars. The former will display anything deemed to be a valid plot on first scan; the plot-extracted radars have to see a plot on at least three consecutive scans before they'll display it. For things like gliders that may appear fleetingly on only one scan, this inevitably means the newer radars will be giving a lot less information on this type of target to controllers. For those providing ATSOCAS that can be a significant concern.
It will be particularly interesting to see how the RAF deals with this issue with their shiny new STAR-2000s.