340-600 climb performance is a tad better than the gentlemanly C2 powered -300. For example, at 370t at ISA +10 it will take about 31mins to climb to FL330, (Cathay has a MTOW of 375t and Virgin 368t). -300 under the same conditions @ 257t (C2) is about 37mins (C4 powered -300 @ 270t about 34 mins. Power to weight ratio on a 370t -600 is about 3.7:1 and on a 270t C4 powered -300 about 4.3:1, and a 257t C2 -300 about 4.5:1, approximately!