I finally ran the 4k time-trial and achieved a 16:58 time. I was supposed to run last weekend but my cold made me postpone it one week. And because of that, it was a run under not the best conditions. Although I started at 21:30, it was 30C and very low humidity levels. Besides that, the park was crowded yet. I ran the usual course and here´s the splits.
Not exactly what I hoped for, but it was my best for now.
Based on this time, I think that a 4:25 and 4:15 for the 2000´s and 1000´s would be a good starting point. Let´s see what TheEd has to say.