RRS Career Prospects?

[Commander Philthy]

I've been enjoying the RRS missions and have graduated to a Tier 6 Contractor. I like the perks such as complimentary refueling and RRS Service (Which I keep trying, but am always told nothing needs fixing.) and the equipment package (but I've got everything)
My question is, how many tiers are there?
What other perks are coming up?
If there are higher tiers, do they bring new missions?
Just so I know whether to persevere or have a go at something else for a bit. I've noticed that if you don't work for them for a while, you drop back a few tiers.

[Norby]

There are some info in the RRS Group Missions page.

[Commander Philthy]

Ok, cheers Norby.
Has anyone made it past tier 6?
Are there any more company perks to be had?
Don't worry about spoilers.