A tune up race this Sunday question

This coming Sunday in Houston is a 26.2K race that I'm treating as a tune up for Houston, 9 weeks away, to see how my training is progressing. In past years as a hopeful 6 hour marathoner, I just had to pray I could make it to the finish line at a 13:45 pace.

This year, as a result of losing 30 pounds and a couple other important changes, I'm faster. I did an 18 mile long run two weeks ago where the 1st nine I did at a 13:07 pace and the last nine at a 12:42 pace (I've been intentionally trying to run the 2nd half of all my long runs as a negative split). The weather was in the 40's and my average heart rate was about 65% of max.

So, I'm sort of thinking I can do Houston at a 13 minute pace, which equates to about a 5:40 marathon. My question relates to McMillan's pace calculator. Now that I have a pace other than what it takes to beat 6 hours, do I look McMillan by inputting my goal marathon time (5:40) and the pace for a 25K of 12:30 is what I should be targeting for Sunday?

And if y'all have any other recommendations as to pace, I'm all ears. Thanks for your time.

I think you could do a 12:30 pace 25K you just did 9 miles after already running 9 just slightly slower than that. Either way I don't think you're at a risk of blowing up at that pace and if you're close but didn't quite hit it that's not a big deal usually (unless you make it one).

For marathon pace I have learned to go by feel and to start at a pace that feels very sustainable. If the weather isn't right, you're ill, or whatever else, you need to adjust to what feels right then.

But isn't it a little bit too early?

Apparently your training is working, keep doing what you are doing, oz.