My Amigo fits my big boy very well, though I have had problems with the make itself- but it's normally a well recommended make so hopefully I had a one off! (Sorry, was that much help!? Lol )
Shires typhone - I have them in weights from 100 - 300 and they fit our Clydesdale and gypsy cob very well - good deep rugs with plenty of neck and shoulder room. Farra is nearly 17 hands and she has the 7' as they are generous.
I find the Amigos too tight round the neck for our chunky girl. I also find Weatherbeeta rugs excellent for large chunky types.
Yeah actually ditto on the weatherbeetas, my little lady isn't huge height wise but she is a draught horse and very chunky, and the weatherbeeta fits her really well, if anything it has extra room as opposed to being too tight!
I'd look at Weatherbeeta and Premier Equine. The depth of the PE rugs are unbeatable if the cut suits your horse.
Rambo amigos are a joke for big horses - the x-surcingles don't even meet on my ID. The only rambo rug that I've got to fit my boy was their heavy weight TO Rambo Excel - made for the larger sized horse but don't often see it advertised now.
BTW my big horse is Irish Draught just over 17.1hh
Premier Equine rugs are fantastic on the big horses, they have nice depth, well worth looking at, also I have Amigo on my boy and they fit well too.... 17.2hh IDxTB