Flickering

[steve.ledger]

Bob, one thing might be worth a check, have you changed anything in Options under the Tune-up tab? Screenshot shows the defaults for this setting on my PC.
(Edit: I notice your OP you stated "My percentage of memory is still set at 25%" - is this what you were referring to?)

Though I played around here and it didn't seem to make any detectable difference.

As I now understand it, display problems in Xtreme are almost always due to faults within the program - not the video drivers. Nearly everything you see in an Xtreme window is rendered by Xara's own routines, the image is then sent to the screen by the video drivers. This the only major involvement by the video drivers and is so simple that it's very unlikely to go wrong.