Checking guest perms

I know I'm probably missing the blatantly obvious somewhere, but is there an already existing lookup to check the guest read perms of a board/forum. I know there's the $pun_user['is_guest'], the $pun_user['g_read_board'] vars, but there doesn't seem to be a generic way, (already there), for checking guest read perms, without a user actually being classed as a guest to use the $pun_user reference point. If that makes sense, have I missed something blindingly obvious, or would I need to incorporate an additional db query to achieve that?

Cheers,

Matt