I recommend a Shimano Stella 10000SW w/ 5.8:1 gear ratio for casting. If you are targeting bluefin tuna or cow yellowfin, get the Stella 18000SW instead for line capacity. Slap some PE-6 line on it and you're good to go. Forget about the surf reels, fireblood, waterblood, bla bla. Just stick to what's proven and works.
Most of my fishing is for, GT, Tuna, Cobia & Kingfish, nothing more than 100 lbs, line is PE 8, Lures not more than 150 grams, using a butt joint 8 feet spinning rod with 26 lbs max drag.
How much line capacity do you need, and are you always going to use pe 8?
If you hadnt said GT and pe 8, a Stella 8000fa(pre 2008) and a 10000sw(2008 and newer) would be perfect. But with GT's and pe 8 as a requirement the 10000Fa and 18000sw would get the nod (also heavier)
Biggest things are making sure the rod is sized to load up correctly, using proper technique, and practice. So, like Doug was saying, if all of these are OK, any of the high end offshore reels should be fine. Surf reels are just not up to the high drag required.
Having said that, here are 3 ideas (just ideas) to get an extra few yards....
Go with smaller 8000FA, 8000/10000SW frame reels if it has the line capacity. The smaller diameter spool should create a little less line slap at stripper guide possibly resulting in longer casts.
If you can spring for the extra jack... Get the newer SW series Stella. They have the improved lip design that's supposed to help casting. I haven't tested them head-to-head since I only have new 20000SW and don't cast with it.
Get the best PE6/8 line you can afford. High-end PE that's intended for casting should be smaller and softer. This should help with casting distance, (if it doesn't get wind knots) and help make sure you get more onto the smaller frame 8000/10000 reel above.
"I'm looking for a long cast offshore reel, been searching & it seems surf reels are the only ones with longer casts. Help plz!"
This question implies a comparison to conventional casting reels. If we're talkin conventionals then reels that completely disengage the spool are going to be some of the best casting reels. And with good technique, you'll be able to hurl some poppers and iron a good distance.
The Avets spin forever. The Avet LX and JX are excellent casting reels and will fish 40-50lb really well. If you're looking for something a little heavier the Avet HX (narrow) will fit the bill for 60lb. If you can find a Baja Special, that's also a worthwhile acquisition. The Diawa Saltist 30T is also a good reel.
Using a spinning reel to cast has it's advantages like avoiding bird-nesting your line. Regardless of how good a caster your may be or how educated your thumb is, chances are if you cast all day long, you'll run into bird nesting your spool and it won't be pretty when that big YFT smashes into your lure while your fingers are trying to untangle the mess. It is highly recommended to use a spinning reel for distance and continuous casting.
I just sold an Avet JX that I magged for casting. On a 12' surf rod I could hurl it farther than any of my spinning setups. On the 7-8' range I could cast the spinners further.
I really like the JX for casting, especially on the beach!