I lost in the tutorial but after I finished it I went straight to diff 7/7 and won. I did a Diff 7.3 game which turned out to be too easy, and then I did a Diff 10 game with a ridiculous amount of cheese enabled, and in retrospect that was way too easy too.
There's been a lot of power creep on the human side, but most of the compensating buffs on the AI side have been to harder difficulties only. Ergo, Diff 7 is rather easier than it used to be. It can still kill you if you make mistakes, but you're not going to get into unwinnable situations unless you have a lot of minor factions or AI plots cranked up high, or pick hard AI types.
Don't be afraid to challenge yourself, basically. You may be able to handle way more than you think.
If you have a good handle on gate raiding, how to set up turrets to defend against waves (see Kahuna's Super Cat guide if you need defense help), and how CPAs work, you can probably handle 7/7.
