In this work we ask whether and to what extent applying a predictor of a publication’s impact that is better than early citations has an effect on the assessment of the research performance of individual scientists. Specifically, we measure the total impact of Italian professors in the sciences and economics over time, valuing their publications first by early citations and then by a weighted combination of early citations and the impact factor of the hosting journal. As expected, the scores and ranks of the two indicators show a very strong correlation, but significant shifts occur in many fields, mainly in economics and statistics, and mathematics and computer science. The higher the share of uncited professors in a field and the shorter the citation time window, the more recommendable is recourse to the above combination.