Big4 Rx FT or Off-cycle at EB? (London / UK )

I'm interested in Rx and I have a FT offer which I'm due to start at a Big4 Rx this Sep.

I made it to the final stages of a BB and an EB as a non-target this past year for FT roles despite only having Big4 experience, but never got any offers

If the oppurtunity arises to take an off-cycle internship (either through OC recruiting or cold emailing) this year/start of next year at an EB and try and convert it to a FT offer for next year instead of taking my current Big4 FT offer for this Sep - would that be wise or am I just getting too greedy?

I know its not impossible to lateral after 3 years and probably the safer move, but I was hoping to land a banking offer now and exiting by then

Also what should my plan B be if I take an Off-Cycle and dont get a return offer, apply for another OC internship?

Thanks in advance