as always, better try before you buy. i tried 5.4 and 5.2 and found i much preferred my beloved celeritas. i only had a go in pretty light winds and almost no waves.
I also ride a Celeritas and love it. I've never tried a T-Rex and am not particularly interested in it. But I would be very interested to hear why you like your Celeritas more than the T-Rex.
I tried the 5.4 as a quad. Found it hard to jump on flat water and it felt quite big in the air. It is very fast but I found it quite hard to go upwind, which is probably a lack of ability on my side as everyone seems to think it shoots upwind. I am not used to quad fins. Maybe a bit more time with the board or a switch to thruster would have solved that.
Then I tried the 5.2 as a thruster. Jumping off flat water was super easy and in the air it felt perfect. But at landings it was pretty small. And when I tried to jibe into some weak waves it stopped planing almost instantly when the kite stopped pulling. The celeritas just keeps going in those conditions.
When I went back to the celeritas, everything felt just right. In the last days I spent a lot of time on my tyrant and that was awsome, too.
Good to have a choice. For me, the more traditional slingshot shapes fit better for what I am doing at the moment