The following two plots show the simulated GPI Strehl performance as a function of the AO Guide star magnitude, assuming median seeing (IQ50). However, it is unlikely that the performance would improve in IQ20 conditions, because GPI isn't designed to run slowly to take advantage of slow seeing. Further, performance at I=10 would be very sensitive to the read noise on the wavefront sensor. The latter is known to be a function of environment and we do not yet know what it will be on the telescope.

Plot of the simulated GPI J-Band Strehl performance as function of AO Guide Star magnitude. Original size image can be found here. The raw FITS files from the simulations can be found here

Plot of the simulated GPI H-Band Strehl performance as function of AO Guide Star magnitude. Original size image can be found here. The raw FITS files from the simulations can be found here