Look, i have experience with all 3, the major difference with the fierce/sargus and the battle is the ht-100 drag system, well the great thing is that you can order the battle drag washers to fit the fierce and sargus, its the ONLY difference in the sargus and battle, it is well worth it to do this upgrade as well, each washer is $1.25 in the 3000/4000 it takes 3, so less than $4 you got a battle...
I have a Sargus and after 2 or 3 years I can't in good faith reccommend it to anyone. While it is a decent reel for the money, IT LOVES LUBRICATION. I have to clean and lube that reel 3 times as much as I do my battle or any shimano reel I own.
Well I want a reel that I can use for reds, use it in the surf on a longer rod, or take it on a buddys boat for cobia. I dont have a lot of money to spend and am looking for something where I can get the most use out of it. Does the 5000 series seem too large?
if you want and will use it for cobia and big drum, get a 5000, i have a battle 5 as well as 2 3000s a few pursuit/battle 4s, and a sargus 7 and really all i end up using are my Battle 3000s for everything! it is just the perfect size if your doing inshore fishing for reds and flounder, if i plan on hitting a pier or surf I may use my 4000s, only very rarely do i use my 5000, although i do love the oversized handle on the 5 if only it would fit on a 4! i just find casting continously say for drum it far to heavy, but a 5 would be fine if you just plan on soaking bait way out in the surf. If your worried say a 3000 wont handle a nice red, no worries...Paired with say a shimano teramar inshore it handles them just fine
The 4000 will do all you need. If line is an issue buy a spare spool and swap rods. I have caught several drum in the surf and off the boat with 3 and 4s. I like the 3 for inshore and throwing artificals in the surf. Live bait and soaking baits I prefer the 4s.