Nice work there Khyron, always helpful to know the exact numbers hidden in that comm chair :P
In a 6v6 its pretty easy to hold 4 RT's, 2 guys holding vent, 3 head to heli and cover both the res there and flight lastly the commander in base builds armory/arms lab.
It would make sense that since the aliens have a comm and probably an early gorge, the most that could attack us early on is 4 skulks, chances are though that they will split up into small groups making it easier for us to defend.
Because of how unbalanced it gets after aliens get fades a lot of the time the main marine objective is to stop that 2nd hive going up, ideally you would hold those 4 RT's until lvl 1 armor and GL's are researched then attack the building hive. Also to save some time and resources I'd say ignore upgrading shotguns, they're main use is to down fades, our aim should be to shut down the aliens b4 they get that far.
That being said, I think its worth the extra 30 seconds to generate the res for an early obs, beacon is a game saver esp if were off downing their 2nd hive meanwhile they come and wipe out marine start...
cant wait to see what the new build does for ns2, hopefully its out soon