I’m enjoying my SLX and would highly recommend it but I’m questioning the line capacity.  It’s supposed to hold close to 105 yards of 40 lb PowerPro braid but I can only spool 63 yards of 50 lb. of sufix 832.  The line size is almost the same diameter and I have the spool filled to the top.  The issue is I can throw a frog and empty the reel and have a hard stop ware I tied into the spool.  I bank fish mostly and need to get some distance sometimes. Is this normal for manufacturers to be this much off on their capacity rating? Maybe I’m missing something.

I don't have or ever owned a slx reel, so I have to ask, are you keeping the line taught when you spool it up..? Keeping tension on the line helps it to lay flat on the spool. 

You'll never get what the company calls max line capacity. They get those numbers in the factory perfectly machine spooled under perfect conditions. Every line also differs in diameter. What a company calls 120 yards of 12lb line is specific to the brand of line used.

I agree, companies like to use the best case numbers for everything.  I just thought it was odd that on their website it says it will spool 105 yards of 40 lb. powerpro at .012 inch diameter and i am trying sufix 50 lb. 832 at .014 inch.  I spooled it tight and to the top.   Maybe for this application I need to jump up to a 200 size spool.

Some quick math... 105*0.012 = 1.26 / 0.014 = 90. So just in theoreticals you should be able to fit 90yd. It is possible you didn't spool it tightly enough. It is also possible the 105yd @ 0.012 number is a little overstated. My guess is a bit of both. You're really bombing that frog though... I wouldn't be very confident in setting the hook at 60yd as it is so any further would be pointless for me, personally. But if you have to cut line off every now and then, you are losing that capacity and maybe at some point it would be an issue for me, obviously for you as well. 

I have 65lb Power Pro with mono backing on a SLX. I can bomb some heavier swim jigs out pretty far and have never seen the backing let alone see the spool.

My biggest concern is with break-offs. Line capacity was fine until I had to cut about 20 yards off due to a nasty snag.  Thats when I was hitting the end of the line often.  Froggin with a 65mm frog was bad but when your throwing a 1 oz. weight on a t-rig that abrupt stop isn't fun.  I tied a uni to uni and filled the spool as much as I could.  Then I reversed the line so the connection knot was closer to the end of the spool.  At least it will give me a warning when I'm getting close to the end.  When I flipped my line over is when I was curious to see what the actual capacity is and paced it out.  It's not like a bass is going to spool me with 12 lbs. of drag locked down so it's not the end of the word.  Tight lines...