As a vocalist, lemme tell ya, Toshi's voice is HARD to emulate.
The hardest song, interestingly enough, is Rusty Nail. The verses are fine, but the chorus is suuuuch a pain in the ass. I.V. is relatively easy, Jade has some high notes that are not so easy all the time. Older Toshi singing tends to be easier because the vocals are a bit more rough, more metal if you will, so it's easier to get by with "Cheating" with more aggressive vocals since it constricts the vocal chords a bit more.
Long story short, Toshi is in a league of his own for the most part. =P