I made it with Monkey Shoulder, Carpano Antica, and Alvear Solera 1927 PX. I added 7.5 ml of water as Simon suggests, and liked it.

Variation:

2 oz Hendricks Flora Adora
1 oz limoncello
1 oz lemon juice
1/2 oz St. Germain
1/4 oz simple syrup (mint infused if you can find it)
6-8 large mint leaves
(Optional) 1 dash each Fee Bros. lemon bitters and mint bitters, or 2 dashes Bitterman's Boston Bittahs

A note on blending bourbon and rye: Triticale is a grain that is a hybrid of wheat and rye. Some distilleries are beginning to make whiskey from it. I've found that Dry Fly Straight Triticale whiskey makes a very nice Manhattan.

I agree with the 2:1 ratio and the cherry syrup (I typically add about a barspoon). My favorite vermouth is Carpano Antico, and my favorite whiskey is Angel's Envy or Jameson Black Barrel, but to my taste these proportions work well with nearly any bourbon, rye, or Irish and nearly any red vermouth.