My (26er) Rocket was a medium and, like yourself, I’m bang between medium and large.
The current (UK) trend is longer frames (like that Mondraker that did ok at the Worlds the other week). Run with a short stem. Really depends what you fancy, I never thought my rocket was short (although I’ve come to wish my mk1 Soul and mk1 Solaris were both a little longer due to having a light front end when climbing steep stuff).
I will revert to my standard answer on these threads though, phone Cotic and talk through things with Paul or Cy. They, funnily enough, know what they are talking about. They are very approachable and helpful, they don’t want to sell you the wrong size either.
Sorry: ETA – I’m 6′