No the specific experience I was recalling was of a line I found on a reel I bought off the Bay (a really nice Marquis 5WT) which I bought from the UK. No idea what the brand is.

The reel and the line looked unused and the line was spooled with insufficient backing and not properly set up so it is 95% sure that this line was sold to a beginner......who probably gave up fly fishing. But that's speculation.

I understand that you actually have a suitable application for this style of line. I myself bought a few Barrio SLX lines with a specific river in mind with high banks where I thought a spey cast and swing through the run might be a fun (if not particularly productive) technique. This is a river in Bavaria with big fish that take big flies where a 6wt is in order.

What I can tell you is that there are few situations here or in the UK where swinging small flies in trout streams (4WT) on the end of a shooting head is going to be an effective technique. You need a DT or longer WF so that you can mend and maintain a more or less dead drift if you are fishing small soft hackles that imitate emergers or nymphs. You might at some point want to retard downstream progress to simulate emergence but you don't want to quickly swim the flies towards the bank as happens on a classic swing at the end of a shooting head unless they are imitating minnows and/or inducing an aggressive response.

Aggressive line for aggressive fish

Fly line descriptions went to hades in a picnic basket last decade - the combination of clear tips, extreme tapers, oversize grain weights under-rated in AFTMA number.
You really have to study the line tapers to figure out what you're getting.
That said, I like the long front tapers on my para inshore rods, and found the short front taper and long back taper on Cortland Salt Guide to be the best possible line to get everything from CGR 7/8 (otherwise, the rod fishes well in close with any line).
But I evaluated that using my arsenal of Teeny lines, old Rocket tapers and newer long-front-taper Redfish line to work that out.

Modern fly lines are like "relaxed fit" jeans...

If you're fat, you can still tell folks you wear a size 32, even though in regular fit, you would be wearing a 36.

My definition of aggressive isn't the length of the head, but that it is front loaded. The weight comes early in the head, so a very short front taper, to the widest part, and then tapering back (how long doesn't really matter) to the running line.

They are good for shooting, and turning over big flies. Not good for dry fly presentation and awful for roll casting.

The opposite would be a triangle taper where the front taper is 30ft. Great for presentation and roll casting, but can't turn over a heavy streamer worth beans.

My general feeling is if you are getting into aggressive fly lines, you might want to consider spinning gear.

Clarkman,
Ok, if I was fishing for musky, chucking dead chickens, I would definitely use something that would turn over the fly and leader. But after half a day, I would probably switch to a spinning rod to save my shoulder.

What Randy's describing, roll-cast, back-cast, shoot is what requires tuning lines and rods.
You make most fly rods turn over most lines, but you can only make the cast above if rod taper, line taper, and grain weight are properly balanced.

Clarkman,
I fish 1/8th oz leadhead marabou jigs or heavy, bullet head wooly buggers on a 6 or 7wt. And yes, getting the line to the surface is fine, but they sink rather fast, so you do need some mass to flip them out. When your line straightens out and then a second or two later your fly goes "ploink", it's time to consider a spinning rod.

I should fish sinking tips more, but when I'm on the water, I fish what I have. And these are the flies that a long front taper have a challenge flipping over.

Ron beat me to it. sinking line, unweighted fly (weight kills the action I'm after). easy peasy.