Or you could just nab the bits of Quakespasm code I stole to get hor+ working so there's proper aspect no matter what if there's 4:3, 16:9, 16:10, 18:4, 24:1...

Aspect is a very overlooked thing in Quake engines - have you seen how many 4:3 stretched 16:9 shots are in the Steam Quake gallery?
(q3 has vert- btw, wish it had hor+)