Agree with Ola & Floyd. I use iS122, but I've sailed 101 and 111 on ocassions. Sail range 6.7 - 8.3 sounds like iS111 territory, but it's a lot of range and you have to choose which end (high or low) is more important ... If you're light (check) and 6.7-7.5 performance is priority (check), then go for iS101.
To answer your question, yes, a lighter sailor can benefit from somewhat larger rig on the same board, in conditions where a heavy sailor feels that gain is zero. I wouldn't choose 8.3 + iS101 as a good lightwind combo, but I'm 86 kilos.