that all sounds about right, depending on how fast you drive though.
my run to work is just under 35 miles, with about 4 miles being 'urban' and the rest motorway / a road if i drive around 70 i'll get about 52mpg average, going home i'll get about 48 as its busy getting out of town where i work.
if i do the same journey at say 80+ then i'll get about 45-48
it depends on how fast you drive, also thought 18's are going to cut a few off too