I concur with Bam here, people often underestimate the strength of tippet. Can't say I've landed 20" fish on 7 or 8X but I've landed 8 Erie steelhead on 5X, granted this 5X was rated at 5.7lbs so not terribly impressive. The 18 inch brown I pulled out of the Little J this year was on 6X AND I was tossing a 4.0mm mop that should have snapped off by just casting it.
The only problem with fluorocarbon is that it has near zero stretch, so once it reaches its breaking point it just snaps. It can be tough when using lighter tippet as a fish can rip your fly off when hook-setting because the tension is too great (thinking of my May Penns trip this year).
I also put more wraps in my clinch knots when using lighter tippet.
Shameless plug: I am madly in love with Cortland's fluorocarbon, really great but expensive stuff. I can't justify it for stockers around me but when making a trip to central PA or the Delaware the 5X is my go-to. Cortland's diameter ratings are often 1 lb. or more (1.6 pounds more than Orvis Mirage when dealing with 5X) than other brands in the same diameter. I'd have to get a micrometer to really see if the diameter is exactly what it says it is, but the tippet "feels right" for the advertised diameter so I really don't care that much, Imma keep using it. My Trout Hunter tippet gathers dust...
Ultimately being intimately tuned in with ones gear can allow lighter tippet usage, just be aware the margin for error is greatly reduced when using this tippet, and you will lose flies and fish.
Lightest I have gone is 7X (Cortland, so 2.9 lbs. of breaking strength). I just checked their 8X and it's rated at 1.9 lbs. so I could justify its usage. I have used P-line fluorocarbon 2lb. for chubs and would run that on my spin rods when fishing 1/64 ounce trout magnets (I could really launch those!).