Turbulent air penetration speed is used when you encounter Severe Turbulence as stated in the 777 FCOM. "Chop" is not normally severe.
Turbulence penetration for the climb is 270kts below FL 250 and 280kts at and above FL 250. Speed should not reduce below min manouevre if below 0.82MN.
Normal climb speed is +300kts for average weights, so you encounter a IAS reduction.
In the cruise you would reduce to .82MN or 15kts above min manouvre speed.
Turbulent penetration speed increases your max and min buffet margins.
Oz