Actually a bit more than a bit… 
I had noticed a slowdown in the display in V6 when there were large amounts of text objects - such as a large land-planning document with many thousands of notations, so I decided to do some testing on my own. And unfortunately, it turned out to be worse than I thought. To be honest, there are also some problems in V5, but they are different.
First, I used the following quickie script to generate 64,000 number texts in a 3D cube:
import rhinoscriptsyntax as rs
import Rhino
rs.EnableRedraw(False)
for x in range(40):
for y in range(40):
for z in range(40):
i_pt=Rhino.Geometry.Point3d(x*10,y*10,z*10)
rs.AddText("{}{}{}".format(x,y,z),i_pt)
rs.ZoomExtents(all=True)
I then saved the result out as both V5 and V6 files.
First astonishment - the V5 file size is 25Mb, the V6 size is 114Mb…! I expect this is due to the rich text format info on each text object - I can’t imagine where else this difference might come from.
Second, V5 opens the file in about 15 seconds, V6 takes… minutes.
Next, what I really wanted to test with all this:
In V5 I can zoom and pan slowly, but I can still move around in the cube. It does have a bit of a display frustum problem when I try to ZoomAllExtents though.
In V6, the ZoomAllExtents looks better. BUT Trying to pan, zoom, or simply switch viewports is way slower. Very sticky.
I am attaching the zipped V5 format file below for reference, but it’s probably easier and faster to just generate the text with the script inside Rhino - takes just a few seconds. However, it is instructive to actually try to open the V5 file in V6. This seems to react much worse then simply generating the texts in a new file in V6, here it takes many minutes to open as I said, and once the file is open, the display performance is worse than with the generated text (here at least). Not sure why there should be a difference.
Anyway, another one for the “things to check” pile… Just in case, I’m testing with a 980Ti and pretty recent drivers.
64KTextV5.zip (3.0 MB)
–Mitch