1650: pacing question

I just blogged this workout (forums.usms.org/entry.php, but wanted to post my question here on the forum. I'm pretty excited because i just finished a set of 20 x 100 on 1:40 and all my reps came in around 1:29-1:31; the last two were in 1:28 and 1:27 because I had so much gas left in the tank. My total yardage was 4400 today (1200 warm-up, drills; 1200 drills, cool-down). 1:40 used to be my BASE, but I haven't done a test set in a long time. The last time I did a broken 1650 was more than a month ago now and the total swim time was a tired 25:51; based on today's workout I would guess it would be a lot faster now. Can I expect my new 1650 pace to be 1:29-1:31? I have to turn in a seed time for the WI SCY State meet coming up in a week and a half and I'm wondering if I should go with mid 25-minute range or whether I should send in my 1500-m time from December (26:53). Some of you know I've only been swimming seriously for a couple of years now and only been swimming meets for about four months, so this will be my first 1650 in a meet context. My training lately has included a lot more speed work, and work on the different strokes (I'm trying to complete the check-off)... I really like the 400 IM for example, but hadn't swum fly before this year. My training the last couple of months has really focused on improving the 100-200 times in back and the 200 and 400 IM. So, I was surprised when I came back to do some pacing work for the 1650 that my freestyle seems to have gotten a little faster and a lot easier.