You could consider some of the medium size, psyllid free, syzygiums, local nursery should be able to advise. You could also think about Murraya paniculata or Raphiolepsis, both of these will grow to 12metres at full height, maybe a bit taller and will generally branch to ground level. To ensure maximum density you could clip them in their early stages.

I'm doing a hedge from White Sasanqua Camellia.
Not going to prune it. Just let it grow!
Should be around the right height. And hardy.
And look great!!!
Or there are lots of pinks/reds to choose from too.

That'll look lovely, I'm planting one out myself actually, replacing a number of Brunsfelsias that I planted about 3 years ago and suddenly 4 or 5 are failing. Dunno if it's a disease or a soil problem, soil is a bit clayey; I think the top soil was removed years ago when they excavated the site. Other things seem to be ok so I thought I'd replace the crook brunses with C. sassanquas. From experience, the 'Paradise' variety are pretty hardy. Camellias are a bit slow though, and 5 to 8 metres might be expecting a bit much, three metres will do me and I reckon 4 metres is about as tall as you could expect! In the cooler parts of the country, I'd also consider C. Japonicas; flowers are bigger, though the growth rate might be a bit slower.
Best of luck
B