Could GoTG pass 300m? It's been having great week days and its weekend holds are pretty great too.
And that's a pretty good hold for TMNT indeed, seems the supposedly terrible word of mouth isn't hurting the movie too much.
Yes.
GOTG is actually tracking pretty closely to Iron Man 1 so far, with Iron Man doing better on weekends and Guardians on week days. Iron Man will probably pull ahead going forward, but Iron Man made $95M after this point in its run. Guardians need $76M to hit the big $300M mark.
It's not a lock or anything though. $280M is basically a lock, and I'd give Guardians a 65% chance of beating Man of Steel's domestic take. Next weekend will give us a clearer picture. It needs a sub 40% drop to have a reasonable shot at $300M.
EDIT:
domestic totals for Iron Man 1
After Weekend 1 - $99M
After Weekend 2 - $178M
After Weekend 3 - $223M
domestic totals for Guardians of the Galaxy
After Weekend 1 - $94M
After Weekend 2 - $177M
After Weekend 3 - $222M