That depends on what your streaming and the settings you're using.
$300 well performance looks something like this
rx 5700 $320 " $280 for Black Friday/Cyber Monday"
RTX 2060 $350 "$320 for Black Friday/Cyber Monday"
1080 Blower style $290 used
1070 TI $250 used
1660 TI $274
1070 $190 used
1660 Super $222
1660 super is about 2-3% slower than a TI and 19%-%30 slower than an RX 5700. For most 1080 games at high settings, a 1660 Super is good enough.