No difference on drop links as far as i'm aware, i believe the different bar thickness only affects the 'D' shaped ARB bushes.
https://www.realoem.com/bmw/enUS/part?id=DU52-EUR-01-2008-E86-BMW-Z4_30si&mg=33&sg=45&diagId=33_1141&q=33552283743
Realoem parts catalogue link shows same part across multiple platforms so i'd say it's a one size for all