Hi Bros and Bro-ettes,
I'm about to get a little bit of inheritance money and figure it's time for a new guitar. Currently I'm playing a Gibson LP through an Orange Dual Terror.. I'm pretty happy with the set up/tone.

I'm looking for a seven string (if you want to talk me into getting a baritone, I'm up for it), basically just for that extra bit of tonal range and heaviness when required. Unfortunately it seems that most sevens on the market are designed for bad Meshuggah worship. Basically I want a tone similar-ish to the Gibson, but with an extra string- a real thick tone that cleans up quite nicely too. Another way of looking at it is that I'm looking for a tone closer to Conan and Sunn O))) as opposed to Animals as Leaders and Cloudkicker or whatever the hell.

Budget would be $1000 AUD max, so let's say $600-$800 US price max.

Sorry if this ain't the kind of input you're looking for, but what about getting one custom made by a luthier? No idea what the costs might be over there, but being that you've already got quite a specific picture of what you want in mind, perhaps you could give someone the indications to make the ideal guitar for you rather than wait until you find something that might or not accommodate fully to your needs.

No chance on the budget I'm looking for, I'm afraid..

I think I would go for a guitar that plays good and is well built and has sustain. A huge sound isn't aways determined by the woods and construction off the guitar. IMO the pickups and amp (and skills of the guitarist) are more important than the guitar itself. And personally, when tuned to B or lower, I don't want a muddy super thick sound. You won't be able to be heard. Pickups are easy to change.
For example, the guitar Peter Tagtren uses on Hypocrisy Destroys Wacken looks like a ibanez 7string. Not known for their fat sound but the tone on that record is huge. Partially because of the bass, but that's what basses are for and you don't want to get too much in the way of the bass frequency's.
But these may be personal opinions, I just want to you some thoughts before purchasing something you would regret.

And a tip, if you don't really use a tremolo, stay away from those with 7 strings. Unless you are on a high budget. This is also somewhat the case with 6 strings, but that extra string really is a pain in the ass with a budget tremolo.

I personally use Schecter low end price one (bought mine for 420 USD), but always wanted to own one of these:
Jeff Loomis JL-7 7-String Electric Guitar
I think on ebay u can find some (without FR) at 750-800 USD price range. SO far (4 years already) love my guitar

I had a Schecter C-7 Hellraiser and fucking loved it. Ibanez and Schecter make excellent extended range guitars, and you can definitely find good ones in your price range. I'd say try to find one that is made of mahogany, has at least a 27" scale, and has passive pickups if you're going for a more classic Gibson sort of approach. Also, Agile guitars make fuckin' solid sevens that won't break the bank: http://www.rondomusic.com/7string.html

also, have you considered a baritone guitar? A friend of mine has an LTD Viper baritone and it plays excellently. It also gives off that Gibson vibe you're looking for, for sure.

Both Epiphone and Gibson baritone Les Pauls exist, but they are very rare and most of the Epiphones have an ugly iron cross on them. The ESP LTD Vipers are modeled after the SG, not the LP, so it's a bit different. Less crunch and more boom, but probably pretty nice for what you're using it for.