How bright could Gliese 710 appear in 1.35 million years?
WolframAlpha says (to the query "apparent magnitude of star with absolute magnitude = 8.23 and distance = 1.1 ly") that the apparent magnitude of Gliese 170 would be about 0.87 on average. I took the value of the absolute magnitude (8.23) from Wikipedia. You can plug in different values for the distance in the formula and see what comes out. The formula used by WolframAlpha is 

$$D_l = 10^{{m-M \over 5} +1} pc$$

where $D_l$ = luminosity distance, $m$ = apparent magnitude, $M$ = absolute magnitude, $pc$ = parsec.