Good question. Limiting the geography makes for a challenge.
Whiteface is a natural in this regard: long cruising, some steep stuff, usually rink smooth (and solid as a rink, too).
Jay Peak is also a good choice. The grooming is a little less comprehensive, but the snow is much, much better.
Smuggler's Notch and Stowe also have some long-ish cruising terrain where you can let it all out.
If you can afford to jet it out west, though, you'll be in much more prime speed terrain, without a doubt.