Since the forging temperature for 17-4 is 2150-2200 oF (1177-1204 oC), there must be some strength at 1904 oF (1040 oC).
I found only 2 relevant data points, for H1150 condition material exposed for 30 seconds at 1800 & 2000 oF, with YS = 26.0 & 12.7 ksi, respectively. Presuming thermally activated softening, plotting log YS vs. 1/T gives
log YS (ksi) = -1.6328 + 3825/T (K)
At 1904 oF (1040 oC), this gives YS = 19 ksi (130 MPa). This is only an upper limit ~valid for 30 second exposures of H1150 condition, as microstructural changes would occur.