The lightest line I ever spool on my baitcasters is 10lb, everything else is on spinning gear. What is the lightest you have comfortably cast on a baitcaster? I had a customers who come in wanting to use super light line and I have no experience with using anything under 10lb on a baitcaster.  I suggested using  a 30lb braid which is equivalent to 10lb test and a light leader as an option. They want to use very light lures as well. Honestly I couldnt sell them on using spinning gear they would only use a baitcaster.  Ended up selling him an ultralight st croix avid and im still at a loss for words. 

i use 8lb diameter power pro super slick with no issues.

10# is the lowest I am comfortable with, too.

I've got a 5'6" med pwr rod I throw 1/8 oz rooster tails and spinnerbaits with on 6# mono. Other than that rod I won't go below 8# mono with my casting gear. That little rod is only for creek fishing and therefore I'm not trying to cast for distance but accuracy instead.

Coak

Lowest I use currently is 8lb but I have used 6lb before.

i use 8lb on my jerkbait setup other than that its 12lb.

Much of it depends on the reel. You can fish small diameter lines on reels equipped for it. Lighter, shallower spools with easier start up are better equipped than those that are heavier, deeper, etc.

I've used as low as 8 lb P-Line Floroclear with zero issues on a Quantum Accurist.

 

Actually used 10 lb Berkeley Fireline on one of my Accurists a year ago, caught my PB on that reel. Worked well.

 

Currently using regular yellow Power Pro in 20 lb test on my Daiwa Lexa. Works well, rarely digs in, which is what some warn about with lower diameter braid, but it is so rare.

I have four Alphas; two spooled with ten, one with eight and one with six. I just sold the rod I paired with the six, so I will probably respool that one with eight.

I run 6lb on my white bass rig. It's a gas! The dudes at the creek look at me like I'm on crack when I show up with a crappie jig on a casting rod.

I've ran 6lb mono and 20lb braid.

6# Yozuri Hybrid on Curado 50E, Steez 103, Daiwa Alpha 103. 

 

6# Sunline Finesse FC on Airy Red Pixy.

The lightest I have ever used was 10#.  I have 15# spooled on right now.

Ive used 10/2 Power Pro on a couple of reels ABU 5600C4, '03 Pinnacle Deadbolt these arent shallow spool "finesse" reels in any way but get the line on very tight and it workd fine for me.

The lowest non-braid Ive used is 8# Trilene XL

I currently use #10 Yo Zuri on most of my bait casters, but I like to pay more attention to line diameter than anything.

I use 6# Sufix Elite on a Calcutta 200, but it's for drift fishing for trout and salmon.  Tried for bass, but broke off a couple baits on the cast.  Usually the lightest I go is 10#.