I was looking the other day was very upset to find the 8ight-T has disappeared from Losi's lineup...I've always wanted an 8ight-T with the Tekno conversion...Maybe ebay.
Anyhow. Rob is pretty much on the dot. AE springs work great and are cheap. I run 40 in the rear, and 35 up front though. It really depends on how hard you drive it. I don't use the ball diff either. Kept loosing the adjustment on it and got tired of having to take the rear end apart. But that's mainly associated with the fact that I'm insane and hardheaded and use 3s all the time. So I just used RTB silicon on my diff and filled it with 6k oil. Seemed to work nicely for my purposes. When I finally get to rebuild, I'll probably adjust to 7k or maybe 8k just to see if it really makes a difference.
I like the look of 2.8'' tires apposed to standard 2.2's. But your tire options are limited there. Again, it comes down to personal preference and going out and trying different things to see what you like. Take a Saturday or something, take your tool kit, some shock oil, different springs, stuff like that and just go play. While a battery is charging or the motor/esc are cooling, make a minor tweak. There's really no "perfect universal setup." It comes down to driver and his vehicle. Just like with Nascar, F1, IRL. No two drivers will like their cars exactly the same. In my opinion (for what it's worth), that's easily applied here.
Just my $0.02