What's the longest/heaviest you would tow with a 1/2 ton?

Mine was probably the same as yours at 1800 ish (didn't have those different wheels and the higher payload rating though). I wouldn't have tried 8k. I think 6K loaded is about the highest I will go with on a 1500 regardless of how much higher it's rated. The TW is usually 700# or less on these units.