Just a quick idea that I found useful on a 205gti site. They've got a sticky topic listing various 205 parts and how much they weigh so people can get postage quotes just by having a look at a list.
Would something like this be useful on here? I don't have any R5 parts to weigh myself, but if you use the forum collective over a matter of time you should end up with quite a comprehensive list. Just requires a mod/admin to keep the first post updated when a member has added it to the topic.
Just a thought.