Swimming "Race Expectations Calculator"

So being I'm trying my first 500 yards at a swim meet this weekend, I went looking for swim calculators to try to help me predict my time. I'd love to break 7:30, but I don't know how realistic that is.

I found this calculator which states that...

Peter Riegel did basic formula for predicting race time. The formula is really simple as it essentially states that roughly speaking, a person's speed declines by around 6% when the distance doubles.

So I plugged in my 1:10 100-yard time (in terms of meters, that's 91.44 meters) being I just swam a pool-start 1:09 100 against Devon recently:

So converting meters to yards, those numbers look like this:
109 yd = 1:17
218 yd = 2:40
437 yd = 5:35

Which means 500 yards (457 meters) would be around 6:28.

WAIT, 6:28?!? That's under 1:18/100 average!!

I was hoping for under 1:30/100 average, but I don't think I can get THAT far under 1:30 pace!

Maybe it's like that running pace calculator issue I posted about 2 years ago where I noted that I was always faster than they thought if I put in my distance times (to predict shorter races), and I was always slower than they thought if I put in my sprint times (to predict longer races).

I mean, I'd LOVE LOVE LOVE to do a 6:28 this weekend, but I think that's way out of the cards for me. (I'm also nervous to be swimming "blind" - I ALWAYS take my 100 splits on my watch, so it will be STRANGE to not know how fast I'm going during the race!)

And thanks to everyone for their advice. I've gotten a number of tweets, and there were some nice comments on this weekend's post:

Goal #1: don't shit in the pool. Goal #2: finish. Goal #3: don't pass out.

I hope I have the guts to race it hard enough from 100-400 but withOUT going too hard! We'll see how this all goes this weekend!!