ADC08D1520QML-SP Group Delay

I am looking at an application in which I would like to use the dual channels of the ADC08D1520QML-SP to alias sample two RF bands.
Band 1 would fall between ~1190MHz to 1250MHz; and Band 2 would fall between ~1560MHz and 1610MHz. We would have all necessary bandpass filtering done prior to sampling. The sampling frequency we are targeting is ~300MHz, the precise value of which ensures that the two RF bands of interest fall in between Nyquist zones.
My questions are as follows:
1) Given our frequencies of interest, Figure 35 of the datasheet indicates we are well into the roll-off of the analog input bandwidth -- what effect will this have on my signals, particularly in group delay of each channel and differential group delay between the two channels?
And 2) At 250-300Msps, Figure 19 and 23 of the datasheet indicate we are approaching the low-end operating capability of the ADC and getting on the "steep" part of those curves. We only require 4-bits of resolution, so that seems OK, but is there any other effects, again particularly on group delay and differential group delay between the channels of which we would need to be aware?