No personal experience, but check out some of Gordo's old race reports http://www.byrn.org/races/race.htm he went from 11:10 IM Canada in 1999 (first IM) to a 9:25 the next year. He may be a freak, but there's one example of huge improvement in a year. If your endurance improves, race execution improves, you could see times drop. Good luck

I started racing triathlons in 1989. I did a local sprint race on a whim because it seemed cool. I finished about 50th and was about 5 minutes behind the winner. I immediately thought " hey with a little training I can win this thing" 5 years, and a lot of learning, later, I won a couple short course races and thought I had the sport dialed. I headed off to Kona for the first time having never done anything longer than an Olympic distance race. In those days(1994) you could qualify at Mrs. T's and other short course races. Based on my sprint performances against some of the top pros, I figured I would have a great race in Kona and set the World on fire. I did for about 2 hours, then my short course pace and nutrition intake caught up to me and I bonked so hard. I ended up going 11:18 and was really humbled. I remember seeing Dave Scott running back down Palani to the finish as I was running? up with about 20 miles still to run/walk. 5 years later, much wiser and with much more knowledge about training and nutrition I went 9:59 at Kona. The interesting thing is I train way less now than I ever did in my younger days but I go faster. I am convinced the years of mileage and knowing your body allows for continued improvement. I will be 38 this year and I still feel like I am getting faster and making improvements. I know age will eventually catch up with me but hopefully not this year as I am planning on being back in Kona for the 10 year anniversary of my first go round.