New results are added to a recent critique of the high-frequency performance of carbon nanotube field-effect transistors (CNFETs). On the practical side, reduction of the number of metallic tubes in CNFETs fashioned from multiple nanotubes has allowed the measured f(T) to be increased to 30 GHz. On the theoretical side, the opinion that the band-structure-determined velocity limits the high-frequency performance has been reinforced by corrections to recent simulation results for doped-contact CNFETs, and by the ruling out of the possibility of favourable image-charge effects. inclusion in the simulations of the features of finite gate-metal thickness and source/drain contact resistance has given an indication of likely practical values for f(T). A meaningful comparison between CNFETs with doped-contacts and metallic contacts has been made. (C) 2008 Elsevier Ltd. All rights reserved.