Etecs have been been good, had an issue with water in the fuel but that had nothing to do with the engines. Check and make sure your underfloor tank doesn't have any hairline cracks!
With 22" props I get just under 50 knots, thats on very flat water and it would be very easy to end up with the mother of all chine walks. I generally cruise at around 35 knots, with 19" props, engines are running at just over 4,000 revs at this speed, using about 9 - 10 gallons an hour. Thats with the boat well loaded up with divers and kit.
ps If your thinking of going for the etecs, speak to John Price at Ribstuff.com. He came up with an excellent deal for me.