Lots of great info in this thread. Brings back a lot of old memories. I fished 4kg for marlin for quite a few years and my daily record on most marlin in a day was on 4kg. The boat got 23 of which I got 12 all on 4kg using rods and reels mentioned here. No they weren't big, all 15 to 25kg, but great fun. My main reel was a SL20SLH (high speed version) It was fine straight out of the box. I did blow 2 spools up over a few years.
To answer Dustins' question we set drags at 2kg on 4 and had a full spool of 4 out on Marlin and Yellowfin quite a few times over the years in double and triple hook ups. We used full spools of 4kg so that would have been over 1,000yards. We didn't back off the drags and didn't bust off. Fishing with Tim Simpson from Bluewater Mag we were in the position where I was down to the knot with my fish going east and he was down to the knot with his fish going west. Probably one of my best fishing memories as the stretch came out of the lines and tightened both fish arced and turned and we ended up getting tags in both.
Fishing 4kg is where just about all the fighting techniques I talk about re heavier line classes came from. It's a great line class and lots of fun. I wish it was still used in competition here but it's been out for quite a few years in my local area.
Once again, all the info in this thread is great, but then again light line guys are a special breed. :) good luck with it all, wish I was there!