Metal Matrix Composites (MMCs) are known for presenting remarkable properties, by combining materials from different classes. Ni-based MMCs, in particular, are a promising group of heat-resistant materials, targeting aerospace applications. Among then, discontinuously reinforced Inconel X-750/TiC 15 vol.% MMCs are under development aiming the use in lighter, creep resistant turbine elements, aspiring to endure up to 800 °C. However, their microstructural stability at high temperatures for long periods of time remains to be further investigated. To address this need, specimens were produced by both conventional hot pressing and spark plasma sintering, using powders milled by low and high energy processes, followed by isothermal aging. The treatments were conducted at 700 and 800 °C, for times between 50 and 1000 hours. The resulting samples were investigated with XRD and EDS techniques for phase analysis, as well as EBSD examination to determine possible grain coarsening and texture. In addition, measurements of hardness were made to hint at mechanical behavior changes. It was found that, for each different manufacturing process, the amount, distribution and size of gamma prime and other precipitates notably vary during the overaging process. As a consequence, the amount of elements kept in solid solution is also predicted to shift with time. Furthermore, the study shows how distinct initial microstructures, resulting from diverse fabrication processes, differently impact the microstructural stability over long times of exposure to high temperatures.