Dareus would be a nice addition but I think the best option in FA for 5T would be Arik Armstead. His size and strength would completely change our defensive front. It's too bad the 9ers are unlikely to let him hit the market.
While the NT position looks like it will be strong in FA and there are guys who would upgrade us it would surprise me to see the Rams go that route. So idk. As I look through the options on the DL it just seems to me that we'd be better served going another direction and drafting a 5T.
FA positions that look to be very strong that are positions of need for us: ILB, FS, and OG. FS isn't discussed much by Rams faithful as a need but I do see it as such and there are going to be some really nice upgrades on the market to improve our single high looks. Either way I'd be leaning towards those positions in FA if I'm Snead.