oooh good question... really depends how much of a perfectionist you are and what 65'' LED you're talking about. No doubt about it at £1500 the OLED gives you the better PQ, black uniformity, etc.
65 inches is just so god damn immersive tho. IF you can still pick up a FALD LED from last year for <2k that could be the best of both worlds.
A bigger screen is more cinematic, more engrossing, more engaging.. just go to the projector forums to hear more about it! however.. a bigger screen does make faults easier to pick up on.
hmm meh u need to make a decision on how picky you are with PQ in all honesty. a B6 OLED vs a low end LCD ... the truth is the OLED destroys the LCD in everything but brightness, image retention + size.
However size is just a HUGE underplayed factor if you like it. For me its the difference between feeling like you're at the cinema and not. Also with good upscaling and especially with 4k content, the 65 inch TV starts to produce an experience which is hard for a smaller screen to properly compete with.
I'm a personal fan of big screen size as I initially wanted a PJ but decided times have moved so far forward now that u can get a reasonably big TV for the price of a PJ.
if ur not OCD and looking for haloing, black uniformity blahblah.. then a bigger screen will be quite phenomenal for providing an experience that a smaller screen can't emulate.
I bought a 50 inch 4-5 years ago. Wish I'd gone for a 60+ inch screen as i would not have bought a new TV now and would have waited.
Don't forget viewing distances, ideally you want to be sitting 1m from a 55" or 1.2 from a 65 inch to make the most of UHD. Its abnormally close for a lot of people but the majority don't actually benefit from UHD because they don't view close enough.