Unless you’re a lucky so n so, it’s likely to be a huge wait…
I’d plump with the medium whilst its available; remember that the more seatpost you have showing, the longer the top tube gets anyhow; if you’re still cramped, you could pop a layback post on there which would redress the balance
Generally, by the time the front wheel is popping up on climbs, you’re having to hover over the saddle to dynamically adjust your weight anyhow and less than an inch isn’t going to make that much real world difference.
I might be talking guff, but I’m 6’1″ and the only time I’ve had a bike that supposedly fits (18″), I found it hugely restrictive when the time came to drop the saddle and lay down some flatties, whereas the 16″ I have now gives me all of the benefits of the larger bike (along with being a tad more comfortable at pedalling height due to additional seatpost flex) with the added bonus of chuckability when I wanna get rad and to be fair, it sounds like you prefer getting rad 8)
I’m happy to take full responsibility if you don’t love it to bits and even happier to take responsibility if you do (though Cy is probably the man for that)