Thanks, that's very useful and I've learned a lot of things. I only had a brief overlook (the first one is a very long article to read it exhaustively, and now I should be in bed since couple hours ago), but saw enough. The second and third articles are ones I can't access (anyway the third one seems unrelated wiith the subject), and the fourth is ony an abstract that emphatizes the morphological differences between two taxa (and obviously there MUST be differences, otherwise they would be not two taxa, but I don't find them enough distictive for calling the taxa "species"). But with the first article alone, there is plenty of coverage of the subject. I learned things such as:
-what I believed to be species Macaca siberu and Macaca pagensis are actually also subspecies of Macaca nemestrina (tough as they're narrowly endemic insular taxa, the lack of hybridation may raise them to species level more quickly than in northern-southern pig taileds)
-there is an hybridation zone of both taxa (that should imply or at least make very probable that the two taxa cannot be different species. But would be interesting to know if the hybrids are sterile or not)
-genetic research has been done already and the conclusion was to keep these taxa as subspecies, before other authors decided to spilt.
So, despite I wanted to avoid any taxonomy discussion in this thread (but little is what I can do for avoid fire in an already burnt house!), I must be very grateful to you, because now I can have a much more informated base for know about the classification of these taxa.