Looking in the i1Pro data I found this (values in DeltaE 94):
Concordanza interstrumentale: 0.4 DE*94 media, 1.0 DE*94 massimo (deviazione dal standard di fabbricazione X-Rite a 23 °C per la modalità misurazione singola su 12 ceramiche BCRA (D50, 2°)
I try to translate in English: Concordance between instruments: medium 0.4 DeltaE, max 1 DeltaE.
The instrument that we are discussing about has a very good repeatability (Ripetibilità a breve termine: <= 0.1 DE*94 (D50, 2°), rispetto al valore medio CIELab di 10 misurazioni ogni 3 secondi su bianco). This is good, but I would not say that it is very accurate. The average DeltaE 94 error of 0.4 DeltaE is something to think about.
I would also think about what paper and printer you are using: as I told you, if you try to print the same target in different days, on a different sheet of paper, with a new set of inks (and this are not all the variables that can make a difference) you will easily find that for almost all the paper/inks/settings the DeltaE between the measurements will be not so small.
Again: a repeatable instrument is a good start, but I would care about many other variables when making printer profiles. As I told you I am not trying to convince anybody with my choice of the Spectrolino, but you will never convince me that the i1Pro (also if used with the i1iO table) is a better instrument. A few reasons: with the Spectrolino I get profiles that are more accurate in the shadow details and I can use the polarization filter and the UV filter.
Also making the hypothesis that your instrument is perfect and has no deviation (and this is not true, because from the data I have the i1Pro REV D has a medium error of 0.4DE 94 as I reported) the paper and the ink that you are using will never be perfect. Anyway I really don’t find a real world application where an accuracy of less than 0.9 DeltaE average is needed. If you need to reproduce a particular color or you want a profile to be optimized for a particular patch there are several ways do this. But we should know what is the goal that you want to reach. Otherwise, for general purposes profile, there are, as I said, many thing that I would care about, accuracy and repeatability of my instrument are on the list, but they are not alone.
Before getting “mad” with “perfect measurements” I would care more (just to make some examples) about: lighting conditions of the area where the print will be exposed, storage “box” used to store the prints, type of glass and frame, “right” management of out of gamut color, management of gloss differential and bronzing (if needed), “pleasantness” of the profile in a real-world print (accuracy of the gradients, shadow details), etc...