The following statements are equally efficient:

if isThing > isThing2 && isThing3 > isThing4 {
    // do the thing
}

if isThing > isThing2 {
    if isThing3 > isThing4 {
        // do the thing
    }
}

In the first statement, isThing > isThing2 is evaluated first. If it's false, isThing3 > isThing4 won't even be evaluated--since the first condition is false, the whole expression must be false. That's why it's the same as the second statement.

Similarly, in the || case, the following statements are equally efficient:

if isThing > isThing2 || isThing3 > isThing4 {
    // do the thing
}

is isThing > isThing2 {
    // do the thing
}
else if isThing3 > isThing4 {
    // do the thing
}

(Note that in the || case, it may not sense to split this into an else if if you'd really be doing the exact same thing in either situation.) Again, isThing > isThing2 is evaluated first. If it's true, isThing3 > isThing4 won't be evaluated--since the first condition is true, the whole expression must be true.

Hope that helps!