Models of tandem mirror devices operated with a test-cell insert have been used to calculate operating parameters for FPD-II+T, an upgrade of the Fusion Power Demonstration-II device. Two test-cell configurations were considered, one accommodating two 1.5 m blanket test modules and the other having four. To minimize the cost of the upgrade, FPD-II+T utilizes the same coil arrangement and machine dimensions outside of the test cell as FPD-II, and the requirements on the end cell systems have been held near or below those for FPD-II. The maximum achievable test cell wall loading found for the short test-cell was 3.5 MW/m2 while 6.0 MW/m2 was obtainable in the long test-cell configuration. The most severe limitation on the achievable wall loading is the upper limit on test-cell beta set by MHD stability calculations. Modification of the shape of the magnetic field in the test-cell by improving the magnet design could raise this beta limit and lead to improved test-cell performance.