yes there are big differences in sizes but as far as my experience goes its never wrong to size up but mostly wrong to size down.
especially for trousers.
i am 6'4" and i wear trousers from size 2 (older stuff) to size 4.
i like the huge oversize fit. so size 4 is normaly the way to go.
i sell a used yohji yamamoto black wide gabardine wool trouser.
its a fine wooven gabardine wool fabrik.
very wide leg.
leg with 30'
used but good condition.
would not sell it but its unfortunately a bit too small for me.
recently i searched for a black yohji trouser in my closet and took the first i found and i thought wow, why i did not wear it more often? than i saw its the suit trouser i sold to benesyd. sometimes its hard to let things go.