Predicting 1/2 ironman time

Tough to tell what you can do until you actually do one.  That said, I'll throw out a guess and say....

6:30

6:31:01   take it to the bank

You'll probably be faster then.  In my opinion though, its hard to "race" your first HIM, being that its hard to know how your body is going to respond.  I think a better goal than any particular time is to finish, and be happy with your performance.  Go for a goal time your second time out.

About as well as we can guess the weather for the day of the race. 

How important is your finishing time to you?  Would you believe me if I told you you could finish in <5 hours?  You might need to hire a coach, change your training habits and overall lifestyle, buy some new gear, etc.  but it's within the realm of possibilities. 

OK this is fun.  Totally a random guess (obviously), but based on the times you provided and assuming you train well and follow an actual plan, I'll give you 18.2 mph on the bike for 56 miles, and a 1:50 half marathon time (because you seem like a strong runner).  Your swim could use some work relative to the other two sports, but assuming you do the training, I gave you a pace of 2:05/100 yards.  Add in five minutes for transitions, and we're at 5:43:00.  If it's in the high 80's or really humid, add 15-20 minutes to that.  There you go, that's my guess.  And I think that bike speed is a bit of a sandbag.

Let us know how you do.  And here's a fun pace calculator that I used to get your times:
http://www.chicagotriclub.com/info/tips/pacecalc.asp

If you've got access to a coach, one of the first things they should do is ask you what your goals are.  If you want to finish in <5 hours, they should help develop a training plan that lets you do so.  If you can only train 6 hours per week, they'll put together a different plan that's less likely to get you to a <5 hour finish. 

As for training runs.  The longer your training runs, the longer the recovery time.  There's a psychological benefit to running longer than 13.1 (or biking more than 56, or swimming more than 2100 yards) that must be weighed agains the extra physical stress & recovery. 

Not sure if it will help you much, but my plan is to train at a rate that lets me finish Kansas 70.3 at 5:10. It might be a tad aggressive since my RedMan (first and only HIM) time was 5:16:18 and according to people who've done both, Kansas has a more challenging bike course. I'll also need to have some luck with the weather as conditions at RedMan this year were just about perfect.

Anyway, feel free to take a look at my logs and RedMan race report for comparison purposes. Though as has already been stated, so much depends on the individual, weather, course, etc that predictions are tough to make.