Okay, I am in the sort of mood where I just cannot let things go. So...
There isn't any downside to flatting over Jamming, I agree, but I feel this is the same the other way round too. I think both villains call a shove here, and that's why I would shove.
Of course there is a downside to jamming... V2 will most likely fold! That's a
huge downside.
You say "I think both villains call a shove here". Really? What are you basing this opinion on? To be honest, V2 should fold regardless of whether you flat or jam. But he would have to be certifiably insane to call if you jam! I realise ofc that many people play this game terribly. And I do agree that there are some players that might sometimes call here in V2's shoes even if you jam. But the vast majority of players, even the very bad ones, would fold vs a jam. Your board and V1's board will look extremely scary for the guy with JJJ. Jamming would put as much pressure as possible on V2 to MAKE THE RIGHT PLAY (folding). Why would we want to do anything to encourage V2 to make a 'tough fold'? (I realise it is not really a tough fold lol, but the only way we have
any chance of V2 putting more money in the pot is if he is the type of player who considers folding his hand on 5th street to be a 'tough fold')
But really, even if V2 is the type who might sometimes find a suicidal call vs a jam... jamming is still really bad. Because if he is the type to sometimes call a jam here... well then he is ALWAYS calling when you flat. And he is then NEVER folding on 6th street, regardless of what cards everyone catches. So it's not like you are giving him a chance to get away from his hand on 6th street by only flatting. On 6th street the pot will be around £250 and effective stacks will be about £120. The kind of player who would call with trip Js on 5th street facing your board and V1's board is simply NEVER going to fold for his last £120 on 6th street. So you lose nothing when you flat, but you DO increase the chances of V2 making a terrible call.
What do we do if The trips villain pairs up? Are we going to fold in fear of getting quartered?
Errr... no. No-one who sees 6th street is going to be folding for their last £120. And certainly not hero who has a wheel! Also, for hero to potentially be getting three-quartered on 6th street V2 would have to pair up AND V1 would have to catch either a 2 or an A. This is a substantial parlay. And even if this unlikely parlay did occur it is still by no means certain that the 2 or A that V1 catches on 6th has made him a wheel. Besides, even if V1 and V2 turned over their cards on 6th street and SHOWED YOU that you were facing a full house and another wheel... well you would still call since you'd be calling ~£120 and you'd get back 1/4 of a ~£600 pot.
Your hand analysis is spot on, and the maths behind it is sound. Just from experience, the human factor will get in the way. I could go into detail as to why... Might post that tonight
What is this 'human factor' that will get in the way? And what exactly will it get in the way of? Seriously, please do go into detail.