Thanks for your help guys. They do have both models in my local showroom, but at different ends of the store - one in full light by the door, and another further back in a dark corner, so I can't really see them "side by side" to compare.

Is the fact that one is a HX85  and the other a HX92 relevant?  Want does the 2 and the 5 represent?  Is this the 2011 vs 2012 models that Catmambo mentions?

And what actually is the difference between Dynamic Edge & Intelligent Peak? The Sony website doesn't really explain this. It would seem to suggest that Intelligent Peak has an extra "boost" for the local dimming, but it doesn't tell me if either is better than the other for HD or SD viewing. One says the contrast ratio is "beyond measurement", whilst the other says it is "infinite" !!  That doesn't help me at all .. it's just confusing sales talk.

Intelligent Peak LED
Get the deepest blacks and brightest whites possible.

The multi-segmented arrangement of the BRAVIA television's LED backlight gives it the ability to produce incredibly deep blacks and outstanding peak highlights by raising and lowering the light level. LED backlight also enables the television to adopt a thinner profile with higher energy efficiency.

Sony's Intelligent Peak LED Backlight uses local dimming and boost to achieve a dynamic contrast ratio so high, it's beyond the limits of measurement.

Dynamic Edge LED
Save energy and experience contrast that's off the charts.

Contrast is the difference between a good picture and a great picture. By varying the LED backlight, Sony is able to achieve a contrast so high, it can't be measured. LEDs also give better colours, a thinner profile, and higher energy efficiency when compared with fluorescent tubes.

Sony's Dynamic Edge LED Backlight uses local dimming to achieve an infinite dynamic contrast ratio.