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The high temperature viscosity limits (log ηx) implied by various threevariable non-Arrhenian viscosity models were investigated, by fitting each model to 4728 high quality viscosity data representing 336 silicate melts. The models used a global optimization algorithm. It indicates it is reasonable to treat the log ηx as a composition-independent constant, because the log ηx values obtained by free fitting show no clear trend as function of compositions. For each form of temperature dependent equation, a bestfitting log value with lowest fitting error can be found, which is different from the average log ηx value. The best-fitting values are -3.52, -1.06, -2.65 and -2.02 log Pa-s for Vogel-Fulcher-Tammann (VFT), Avramov-Milchev (AM), Adam-Gibbs (AG) and Mauro-Yue-Ellison-Gupta-Allan (MYEGA) equations, respectively. A viscosity model can be significantly simplified and meanwhile ensures an acceptable high accuracy by setting log ηx as derived best-fitting value. [ABSTRACT FROM AUTHOR]