I think Breckenridge now has the greatest quantity of expert terrain in Summit County. The opening of Peak 6 is a quantum leap for Breck. There's still the issue of too many people, and if you don't know what or where to ski, you can find yourself chasing terrain with lousy snow due to wind, sun, traffic, etc. So a guide is really going to help you find the best stuff.
Here's my take on some of the expert terrain:
The Lake Chutes are a great place. I skied Zoot Chute today and it was soft and buff. The entrance can be a bit tricky with rocks and a significant cornice, but it is easier than Crazy Ivans (which is not ready now -- needs more snow because of the huge cornice and consequences of the exposed rock bands if something goes wrong). These lines are in the upper 40 degree range yet relatively short.
Horseshoe bowl is one of my favorites. Lots of steeps in here --my favorite is Lulu which is skier's left. You also have good lines that you can navigate too, but it takes some direction to find them, like outlaw.
Contest bowl is short and sweet. I particularly like King, the steepest line, with the tough line between the two trees that is narrow and a deep trough. Also the Boundary Chutes...
This is all about E Chair. The windows (there are numerous lines here, but watch the exit through the creek bottom -- it is full of holes, creeks, and rocks -- best to have a guide), Inferno, Minecrotch, Eye of the Needle, and Mineshaft. A good thing about E Chair is that it is usually out of the wind.
Whales tale, Magic Carpet, CJ''s, Y Chutes, Art's Bowle, the Dunes. Can be incredible. Steep. And sometimes very wind affected with significant wind slab.
Some incredible terrain in here, but I've not had enough time to ski it to isolate the good from the bad. Hike to the ridge and head North or South. Lots of stuff below you...
A good guide will help you find the goods and provide some tips as well. I can give you some ideas of good instructors at Breck...