120Hz matters if you want native signals to be judder free. This will affect 1080p24 BD movies and 1080i30 concert or doco footage.
HDMI 1.3 matters if you plan on buying those HD videocams that can do xvColor. It'll give you a wider color depth (not deeper/more bits).
I don't know about the DRC but if you want DRC2.5, then you have to get the new XBR5 series. Price difference is US$2000.
Read the press release here.
The A Series
The XBR5 series.
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