About to install a pair of Dellortos. What sort of MPG can I expect? (1600 XFlow)

How heavy is your right foot?

15-35 depending on right foot and engine spec id' say.
my old westfield on a run to scotland did low to mid 30s
1700, 244 cam, BVH, DHLA's, 5 speed box and 3.89 diff. So about 3300rpm at 70 in 5th

high 20's for mine, I'm lead footed!