Go with galvanized steel, or Stainless steel. Buy afew 3/4 and keep them inside the jeep untill you need them or else they will vibrate off and hit someone behind you. The 3/4 Shackles are rated for about 9500 lbs so just stick with that, might also wana grab you a snatch block. You should be able to get both from Warn for a decent price.
Bad signs to look out for in your rigging.
If it looks warped in anyway TOSS IT and buy a new one. Specially if the eyes that hold the pins are stretched its time for a new one, better to lose 5 bucks then to lose a limb or life. Riggers call that the "Fish eye" on bad shackles.
Wear on straps is common but most straps are installed with a red thread on the inside. If you see this red/orange thread cut the eye of the strap and BUY A NEW ONE! Make sure to cut the eye so that it is not useable any longer.
Same with Shackle if its warped or in bad shape toss it and buy a new one, snatch blocks have a lot of strain on them when pulling a load and if one goes its lights out.
Every night at work (my morning) I would go through our gang box's and review our rigging with safety tape checking our shackles/straps/snatch blocks/come alongs/numatic winches to make sure they were safe to use that shift.
If you have a tractor supply store, check to see if they have the rigging handbook. And read up on it, you will thank your self later. Shows the correct way to use rigging and what loads everything is rated for. If you love math this book will make you tipsy, if you like pictures it has them also.
The hand book should include afew pages on knots which comes in very handy if you remember them all. Should have all these in it.
I could go on and on about rigging.