Without wishing to be a downer, my best 5k form was 19.22, but I wouldn't have got close to sub 1.30 in a half marathon at the time because I didn't have the endurance. If you aren't worried about flaming out, go for it though.
I suspect it’ll be closer to 1:45 tbh. Might go out at 4:20/km one day soon and see how far I get. It’s a bit less hot here now so not such a health risk.
Without wishing to be a downer, my best 5k form was 19.22, but I wouldn't have got close to sub 1.30 in a half marathon at the time because I didn't have the endurance. If you aren't worried about flaming out, go for it though.