Yes, US gallons. 42 is pretty reasonable... I wouldn't expect much more from such a large engine and large motorcycle... although some do better with a more recent/modern ECU flash than what I am using. 42 is mostly highway and some spirited acceleration (but mostly just cruising).
It can certainly go DOWN from 42 when I ride aggressively (lots of unnecessary throttle/etc), but that is pretty rare for me.
I think my G37S gets about 22MPG highway. Both vehicles require high octane. But at least the G37S has a 350 mile range; the C14 is only about 240 (which I think is too low for this class of motorcycle).
A lot depends on where you are and local traffic conditions.
Here in the UK(especially on the dail commute) the majority of my riding is point & squirt , dart & dive, in & out of traffic.
Best comparison I have is with the Birds (cbr1100xx). Typically in the UK I would be averaging around 36mpg/30mpg(US) on the daily run rising to around 43mpg/36mpg(US) if I was taking my GF out for a run.
On a 3 week 5000 mile holiday in Oz on a borrowed Bird i was regularly seeing 45mpg/38mpg(US) plus without even trying
That said at least the FI Bird has a 24 litre tank instead of the tiddly 22litre tank fitted to these fine machines, a bike like the GTR really deserves a much larger tank (29 litres on the ST1300, the old ST1100 was 28 litres, the FJR is around 26 litres) as even the most ham fisted rider should (if needed) be able to get 200 miles minimum to chicken light
a 26 litre tank with 4 litres reserve would even at my normal commuting MPG just about fulfill that requirement. 28 litres more so (as on my old ST1100 which regularly saw 200 plus and ridden gently 300 miles to chicken light)
