Hi Jack,
The weed died off some years ago and the majority of the barbel went with it unfortunately, there are areas where they turn up from time to time but you really have to put the hours in...and lots of them!...if you're new to barbel fishing and have never caught before I'd strongly suggest going to the Middle first and upping the tally then coming back. 'Monstro' is a great story to get the juices flowing but I've yet to catch any barbel of epic proportions. I've seen photos of the 15's...they're not. Although a couple I've not seen are reported to be genuine, all from the 90's mind you! You're doing extremely well with a 10lb+ fish these days.
If you want to sit in the most beautiful surroundings on the upper it has to be the Lymm AC stretch at Llandrinio, you have a good chance of bumping into fish there...up from the bridge is the Monty and Albert beats, I'd give them a miss.
Leighton is as dead as a dodo, poachers have netted it many times and whatever travellers make their way upstream are soon chased off by the family of otters that reside there. Pool Quay is good for big chub if you're into that sort of thing and some barbel will hang round there in summer and autumn. Buttington holds them too.
There are a few private beats that fish very well, from what I can tell this is simply because the predators are 'shuffled' along by the owners and the fish know it so they hold up in these 'safe zones', there is certainly no bait going in to hold them. Prime game water you see. Costs you a few quid in beer for the farmers to fish these bits.
I've had them up to Abermule but there have been sightings as far as Caersws apparently...people do talk a lot round 'ere after a few though.
Get yourself the Lymm ticket and BAA and you'll be fine. You'll have a bit of the Vyrnwy then too.......now that does have big fish