Many thanks for all that input, guys!
Agree that it needs costing, and that could vary enormously depending on whether the three elements in the mix can be sourced economically. OK, not talking about 50m - that's a substantial run! - but even 50ft wouldn't come in cheap, I guess, for a decent quality close-boarded job. Plus, as stated, that would still give a large surface area for high winds to hit, which is why I wondered about the hit-and-miss method.
Should have said that it backs onto a garage block, hence (a) not the prettiest and (b) will have people trundling up and down it. Height, therfore, would be in the 6ft region, and really needs to be opaque.
Also thought that many people seem to use gabions as features... benches, planters etc, so it would double as a host for some kind of climbing plant down the road (fingers definitely not green so nothing to suggest in that dept!)
many thanks again.... more mulling in order, nothing set in stone yet ( no pun intended!!)
Cheers,
Tim