Yes, to your first question. Yes, to your second question. The cold rolled will have slightly lower notch toughness, provided both steel plates were provided in the same heat treatment condition (hot rolled, air cooled). The problem with A36 with regards to impact properties is variability in impact values based on plate thickness, and steel making practice.

Thanks for the response.  I found a temperature / impact performance graph of the A-36 material this morning.  While it did not list the thickness, it generally showed that it would be in the neighborhood of 10 ft.lbs at -20F.  I'd be interested in 1/2" thick A-36 steel.  My goal is to have at least 4 ft.lb at -20F.  An anecdotal graph I found comparing A-36 to the steel of the Titanic is found at:
http://www.tms.org/pubs/journals/JOM/9801/Felkins-9801.fig.7.lg.gif

If the steel is fully killed, and fine grained, you should be able to obtain 15 ft-lbs at -20 deg F. If the steel is semi-killed, as-rolled, all bets are off, and you could be as low as 5 ft-lbs at -20 deg F.

D2L,
I have seen numerous tests on A36 materials taken from existing structures such as storage tanks.  Usually by the time the test temperature is lowered to +20F, I see the CVN values dropping to the 3 to 6 ft# range.  It ought to be even lower at -20F.  For 1/2" plate one can't assume anything at -20F for A36 unless you buy it with impact tests.

Joe Tank