Deice has brought up a good point. Modern engines aren't really better at converting fuel to power, they just lose less of it along the way.
Small turbines in GA is a pipe dream, but you never know, one day we may be able to get the costs down far enough. Long way off though.
At our high speed cruise of 190 kts we work on a figure of 18L per minute, giving a flow of 1080L per Hour. This is in an aircraft with a MTOW of 12 tonnes, we have around 3000HP so get a figure of 2.77L per hour per HP. Now divide this by 12 gives you 0.23L per Hour per HP per tonne.
A bit gash, but what do you expect here!!