Petrucci for me. The Glass Prison in particular. I might never quite attain the skill to play the arps at full speed, but that earthy, crunching rhythm part just did it for me! As I am also a major swinger to the 7 string.
Although I haven't listened them much at all in years, they were the first on the 7 string scene that I ever saw and heard (apart from Steve Vai but I didn't care for his music at the time). When I first saw Munky and Head holding a Universe in some promo photo, and then listening to their first two records, I knew I had to get one. I didn't, they were too expensive, but sometime later I used half of my student loan on an RG7620 and ever since 6 stringers have been a secondary instrument for me. Fast forward 11-12 years and I am currently saving up for a Universe.
gotta say jeff loomis, ihsahn's latest solo album, and them dudes in periphery did it for me. i'm not a "djenter", not by a longshot (EMG'S FTW HAHA) but the idea of using a 7 string guitar to further elaborate on a composition or extend the range of a riff rather than using it to bludgeon people with the low string appealed to me.
Those are mainly the reason I picked up a 7. I've only had it for 3 months, and I'm already addicted and want 4 or 5 more. I'm tuned for G.D.G.C.F.A.d, may need some heavier strings
Now my influences i'm listening to are purely
WhiteChapel Meshuggah Animals as Leaders Outworld Nevermore Dream Theatre
Initially it would be Petrucci and Loomis, mostly due to watching the live dvd version of Dance of Eternity. More recently, Acle Kahney as I love everything that guy has been and is a part of.
For me it's not necessarily about who as why...but if I were to label a "who" I'd say my 1st baritone (sub drop-d) songs were on DT's Awake album (specifically Lie & Caught in a Web). I didn't get inspiration until I hit the rut and decided to start attempting to re-invent myself. Then, it was & is Jeff Loomis and still Petrucci (to a lesser degree).
For me it was reading up on Megadeth's Chris Broderick. I love Megadeth, but I had no idea they had gotten a new guitarist until I watched The Big 4 DVD and saw him. I then watched some video's of him on YouTube playing a 7 and I was blown away. Also from watching him I landed on Jeff Loomis, and I must say I was blown away even more. These 2 guys are the reason I decided to start playing 7's.