The 54 will probably be in the upper 600's... guessing 680's. That's a guess.
This is calculating that the SL frameset for a 56 comes in at 1,020g. A typical 'light weight' fork coming from a major brand is typically in the low 300's. Let's say it's 320g for our purposes here, which leaves us with a 700g frame in 56. On the other hand, Scott could have come out with a ultra-light fork... which is doubtful unless they've recruited THM to do their engineering... but let's say the fork is actually 280g. That means the 56 is 740g, which makes the upgrade for you pretty meaningless.
But back to the 54. It is claimed at "sub 1kg," and Scott has been pretty accurate with their claims. Let's play nice and say it's 999g. 999g - 320g = 679g frame weight. Guessing.
The question, however, is whether the frameset in the linked article included headset bearings, derailleur hanger, etc:. If that is the case, the frame itself could be even lighter (headset bearings ~60g). You would then be looking at a 54 in the low 600's. Which would be exceptional. But we have no idea right now, which is frustrating.
Whoever reviewed the frame was clearly not a proper WeightWeenie: the weights are provided, but a lot of questions were left unanswered and we can only guess from there. They also completely neglected to take a picture of the frameset on a scale despite providing their own detailed shots beyond the Scott-Marketing-Dept-Handouts. This last part is especially frustrating: this sort of frame is somewhat targeted at the type of person who really weighs everything, if you're writing an article that will be read by that market, you should at least put in half-an-ass's worth of effort and take pictures with scale shots. It really isn't that difficult. The writers have a camera. They have a scale.
EDIT: It really doesn't matter too much though. Scott states two separate frames for mechanical and electronic. The only ultra-light, high-end frame that currently exists which can accommodate all three drivetrain types is the Cervelo RCA. We may have to wait another year before brands update their frames for the 3rd option, just like we had to wait a year after Di2 was first announced/leaked/released and we saw a lot of home-made modifications while people waited for the frame brands to catch up.
|| Other projects in the works.