Ok so here is my update....
I left the beer a little longer that initially planned, partly as I could see a little activity with the yeast bubbling on for a week extra on the ss brewtech chronical (3 weeks in total) and partly as I was busy (I ended up leaving the carboy about 6 weeks). I didn't cold crash and kegged/bottled warm.
I filled 12x 500ml bottles from chronical and 1.5 kegs. The kegs got a full strip down but most importantly I dismantled what turned out to be fiddley poppets in the keg posts (mine are the ones with the little 3 prong things that clip inside the posts) and I also stripped the disconnects (which I've done before) removing all the o-rings and springs and reassembling.
Kegs purged with fresh water, 1/2 tsp k-meta to strip and co2 from the water and then starsan at typical strength and then purged with fresh co2.
I force carbed at high pressure on the chronical batch reaching a decent level after 2-3 days. The bottles were conditioned for 3 weeks using the 500ml carbonation drops and swing top bottle, which were sanitised and co2 purged prior to filling.
The carboy I left a fair while as I was busy and wasn't looking forward to racking it in all honesty. I filled 13 bottles and half a keg or so with the same method. I managed to get a syphon going with a disconnect on the liquid out post of the keg and just left the prv open and let gravity do it's thing which worked suprisingly well.
So the chronical kegs...
First tasting day (2-3 after kegging) the beer was a little sweet, a little hazy (which I was expecting), good apricot flavour from the yeast (verdant), some malt flavour and not much hop flavour (which was expected as there wasn't much added). I was please with the bitterness and sweetness balanace, but the beer lacked a good dry hop so the sweetness was a little cloying.
About day 6 the bitterness picked up in the beer from the early bittering hops I think this was just the flavour devloping probably the interplay with the carbonic acid from the co2 and the bitterness from the hops. This however improved the flavour of the beer dramatically and it tasted far more balanced. I dropped the pressure down to serving around 9 psi.
Over the next 2-3 weeks the beer remained pretty stable in flavour, but then I noticed the sweetness dip and the bitterness seemed more pronouced. Still drinkable and no sourness. The beer was clearing up a little as yeast settled and again the lack of dry hops wasn't going to really give a stable haze. I wondered if the yeast dropping out of suspension maybe was changing the flavour slightly.
The flavour then seemed different over the next couple of weeks almost every time I tasted it, I thought I started noticing a little sourness and bitterness as before a couple of times, but then other times that subsided. I tried to taste with clear pallate before eating or drinking anything else and after both savoury, salty and sweet foods, but didn't seem to draw any parrallels.
Today I'm drinking the same beer, and it tastes absolutely fine nice balanced flavour, the apricot from the yeast is shining through nicely and the sweetness is back to the levels of day 6.
My thoughts so far was that I over carbonated the beer initially and perhaps this has been the bitter sour flavour I've percieved with the carbonic acid interacting with the bitterness of the hops. I also wondered about what I ate or drank before was affecting my perception of the flavour but I tried many things and today I even ate a cookie before which I thought might really make it seem more bitter or sour, but it didn't. So there is definately something going on I don't understand with how the flavour develops in the keg and I suspect this is related to CO2.
On to the chronicals bottles, again the same cloying sweetness in a bottle I tried after a week of conditioning, flavour similar, more malt, more apricot and more gentle carbonation, similar haze to the keg.
After 3 weeks conditioning the carbonation was spot on and the head was much creamier than the keg, the flavour slightly sweeter than the keg but the bitterness had balanced out nicely the same as the kegs on day 6 on to week 3.
So on to the carboy, I've kegged this beer the same, I gave it an initial blast of co2 at 3 bar for about 12 hours, and then I came around to my thoughts around over carbonation so I dropped the pressure down to about 9 psi and left for a couple of weeks. I've just tasted it today and the flavour is fantastic, much more balanced and the head is creamier like the bottle conditioned beer.
I've not tried the carboy bottles as they need another week or so conditioning, but they are likely the same as the others.
I did find a little scudge in one of the keg posts when I was dismantling and scrubbing things. This wasn't visible until I completely dismantled the poppets and even then it was hardly noticable and as I said had been boiled.
I'm still undecided if this was an infection or if it was over carbonation, I think the warming of the beer with a high level of carbonic acid in it would potentially make it seem like its becoming more sour/bitter in the glass and would certainly explain some of the things I've noticed this time. There is still something I don't understand about flavour development or flip-flopping between bitter and sweet and back again within the keg and the timespans these occur over or the impact of co2 on flavour and how that develops or changes (Any links or recommended reading would be much appreciated around this subject).
I will see how things develop with the carboys keg, but overall I've got drinkable beer which I'm very happy with, but I'm still not confident with what the changes in flavour are caused by and how to predict or understand these better, which makes me a little apprehensive about trying a big hop heavy beer again just yet.
Ps the beer ended about 5.9%