Playing a MTT loads and loads of runners we are down to last 350 money starts at 130th so no where near it yet. We are comfortable, infact very comfortable with chips we have around 37k avergae is 21k.
With the chips that you have it is true that you have a bit of temporary breathing space. But with 350 players left there are a significant amount of chips still to play for. If you want to give yourself a shot at winning the event you can't afford to take your foot off the gas for a second.
You have made a speculative call with the J-8 and hit a really good flop.
The original bettor puts 1,400 into a 4,400 pot with plenty of bodies behind him. So I agree with Alex here in saying that his likely holding is far from strong. He could very well have a draw himself and is trying to control the price of the turn card.
You put in a significant raise and the original bettor only flat calls. With almost 20k in this sizeable pot surely an all-in would be forthcoming from a monster hand on this dangerours drawing flop. The flat-call signifies a strong draw in my eyes.
When the 8 comes your hand gets even stronger. If you do find yourself behind, which I doubt, then you will certainly not be drawing dead.
Of course you could fold here and leave yourself with 9k, but you will gambling again soon enough and probably in a situation far less favourable than this. Importantly, the time to make this decision though was before committing a further 16k on the turn. Once you make this bet you are now going all the way. And I for one fancy your chances.