Hi Toby - here in V5, if AA is set to none, I do get a clean crisp ortho aligned rectangles as in your image - I can only get the blurries if I ask for 2x or 4x antialiasing.
Hi Joddy - In V5 there is only one setting for AA, under Options > View > DisplayModes > OpenGL, it is not separate for curves, if that is what you mean.
There is testLineSmoothing, which does do nice things to curves/isocurves/edges and is independent of the AA settings. You can play with that, keeping in mind that this is an unsupported test command that you use ‘at your own risk’.
Hi Joddys- what does the info about openGL and the video card, below the setting, tell you? It may be that your card does not support AA - that is the case on my MacBook Air.