Er... what overhead? You mean of making an array access because that's all it is. @+ and @- don't invoke the $`, $& and $' penalties. Those arrays are just offsets into the string. $-[0] is the offset of the beginning of the string and $+[0] is the offset of the end of the string. Using those doesn't prompt perl to do all the copying that capturing, $`, $&, and $' do. Its just not the same thing.

Granted, I did miss that scalar /g loops only once and in this usage that'd be the only loop ever used. I find myself avoiding pos() after learning that it doesn't survive a local() on the variable in question. That's just style though.