After thinking about the larger turbine wheel in the stock housing question a bit more, I have changed my mind about my previous post. In order to fit the larger wheel into the housing, it will be necessary to bore out the turbine exit. As a result, the exit area will increase (~15% increase for TD04H wheel and ~35% increase for the TD05E wheel). This should allow a higher flow of exhaust gases through the turbine, both increasing turbine efficiency, and preventing excessive back pressure and control issues.
Low-end performance should still be good (but not as responsive as the stock hotside), since the exhaust velocity entering the turbine will be higher than that seen in a TD05H hotside at low engine speeds (low exhaust energy).
Upper range performance should improve over the TD04-19T with stock turbine wheel, both due to higher turbine efficiency and better balance with the flow capability of the 19T compressor.