This is probably going to be uber-difficult to find but if you can get ur hands on the music for a show called No Way to Treat a Lady, u will find numerous songs that are perfect in my opinion. The character of Kit's songs all deal with him being a murderer and are in Sweeney range.
Otherwise my suggestions would be:
1. Apology to a Cow from Bat Boy (very intense)
2. Anthem (or something else equally as challenging) from Chess
3. I'm Martin Guerre ~Martin Guerre (i guess go with this if u want to be Anthony or Toby more)
Yes that's me. No, it's not a Rent homage.