You can get a Stella 10kSW spool for it. Shimano USA says the 10kSW spool will fit the 8kSWPG, but with the added cost ($285 + S&H), you could just as well get a JDM 10kSWPG (No warranty in US though). If you don't already have a Stella 20kSW, you should consider getting that for jigging instead.
Never fished in Miami, so I can't comment there. I would say the 8kSWPG can take anything that you're probably targeting on jigs, the only drawback is the line capacity on that spool. IMO, I would rather get the 20k for jigging even if I am not targeting bigger fish because it's nice to know you have the line capacity to handle them if you ever try for it, but that's just me. After all, you never truly know what you might actually hook up on right?
Not sure about typical drops around Miami either... But can't imagine 8000 with good quality** PE4-5 wouldn't be fine. For GOM, the 8000 is pretty darn close to perfect reel! Just load with PE4-5 line and catch 'em up!
** Keep in mind that PE line tensile ratings vary directly with cost. You can always get something like 64lb Varivas Max Power PE4. It just costs a little more...
I have 20K/600g setup that I really like. It's nice to have for heavy/deep dropping and hunting big fish, and if I was on an over-nighter with one rod, that would be it... But it really is overkill for most day trips and most fishing I do.
An 8000 on a 400g rod would be the ticket for 90% of my fishies!
I have the same question on the 8k. Would the Diawa pe4 (55lb.) be good for fishing the GOM? I am thinking of getting one and figured i could get more line capacity with the pe4 rather than the pe6 and that the pe4 would be strong enough. I would think most AJ's will be between 25-60lbs or at least that's what we usually catch. Or would you guys recommend another brand? I can't afford some of the higher end lines and figured the Diawa or maybe the tuff line would be a good choice.