The 40p ones give wins much more frequently, if they do go up (personally I think they go up more) you will probably get £1 and stop, if its playing good you might get 2 fivers but the best ive seen on a 40p is a £22 top and it was full and only taking 40p wins.
£1 are horrifying for getting a win, thought they usually drop in a cheeky £5 (astras) and hardly ever go up, if they do its either £2 board and stop or they will go well over £15 if they are playing pretty good.
To be honest I prefer the 40p XXXs for gameplay but if you see and old biddy smashing her pension into a £1 XXXs version and leaves it, id be on it quicker than you can say 'lets play bullion bars'.
You'll find plenty of party times my way (skeg) . but there are also lots of a newer versions around of party time which I havent had the displeasure of playing. Lucky strike and harrisons seem the most legit arcades here. I tend to avoid the others.
An arcade near me has got a new bullion bars and a party time, looks really good, but if you see one, run away as fast as you can, if you happen to be on one which is genuinly dropping, run away even more, I tried £55 through a £5 jackpot one with nothing more than a £5 board, run away, run away some more then run away from where ever youve run to.