I'm more interested in grip than mileage, so what follows is only about grip.
- Tourance and Trail Attack. What bothers me is the negative thread pattern in blocks. These tend to wear uneven, so that the tyre loses grip as it does more miles. This can then lead to wobbly behaviour on lean. Just as an example :
- Anakee has a longitudal negative thread pattern, with the same result from new, esp. when loaded : wobbly on angle.
- Battlewing doesn't have these blocks, and is an excellent performer as far as grip goes, but it has problems in the wet.
- Tourance EXP : block pattern, but since the compound is softer (= best grip), it wears more even. Of all GS tyres my personal favourite.
The advantage of larger grooves on GS tyres is that it takes more time for them to fill up with mud/sand. If I'd really need to buy GS tyres, I'd buy Tourance EXP again, because of the excellent grip. I would definitely NOT buy Tourance, Anakee, Battlewing, Trail Attack.
The description of typical GS tyres is usually something like '80% road, 20% off road'. This indicates that they're close to 100% road tyres. The typical GS tyre is NOT suited for real off roading anyway, you'd need wobblies. The question then is : how close are road tyres to GS tyres ?
Last year I drove into a wood on EXP, hoping to bypass some roadworks. To my surprise I was followed by 3 non trail bikes that aren't supposed to go off road, on specific road tyres. One of them a Triumph 1150 Sprint.

They coped well in these circumstances. The trail through the wood got worse and worse. Every time I thought 'surely they'll stop here', they were still right behind me. This made me realise that road tyres can do more than expected.
So I decided to buy road tyres. I was fed up with the uneven wear and loss of grip on GS tyres. I bought Dunlop Roadsmarts. They outperform the typical GS tyres on tarmac, have amazing grip anytime, dry or wet, and are far more comfortable. I'm on my third set now, and I'll stick with them till something better comes along.
But that's just what I decided I want from my tyres. There are so many considerations : high mileage is one of them, and another seems to be the 'look' on a GS.
To each their own

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Cheers !