It isn´t impossible if it´s short like Petrucci´s video lick. I had it in my head that I couldn´t play Bumblebee faster than 220 but my friend pushed me on all the way to 250 but hard to get it 100% all the way. I play Petruccis verision and it´s about 20-30 sec. of non stop ultimate shred.
Still for me I think I could reach 260 (Petruccis video lick) and maby 270 if I really push my self but 300, I don´t think so. But belive me 250 is hyper speed. If I could play any kind of 16-note licks at 250, I would be worlds greatest guitar player but that´s IMPOSSIBLE.
I would LOVE to see maniac shred him self through Paganin´s 5 caprice (mostly 16-notes) at 250. wrrrrooommm.
But, keep the struggle Aiwas.
And about string gauge 0,09-0,45 D´Addario. Very smooth.
Dejan S. No speed limit