I think it's a bit of both. In terms of stamina, there's no denying Pure Boo is still leagues above a dead SS3 Goku and those pages do seem to suggest Goku's victory would only be secured through a full power attack rather than through maintaining his Ki. That said, I believe Goku would only win if he gets the time to charge up a Kamehameha capable of oblierating Boo, his safest bet to also utilise Taiyoken and Shunkan Ido for the right opening. With a rabid beast of an opponent like Boo being far different from the arrogance of Perfect Cell, however, I don't see Boo giving him such an opportunity to do so when Goku's performance hasn't reached the point where Boo feels the need to taunt him like in the above page, plus he could always use his Shunkan Ido to escape if he catches on to what Goku's doing.