With time, paste can dry and/or be squished out and loose effectiveness, specially with direct died GPUs. For more powerful cards use at higher temps, that means about 2 years.Thanks for the link! From reading the comments...and other reviews....it seems reasonably clear that there is no significant advantage to using the sheet rather than the paste. Adding the reported delicacy of handling the sheet, it looks like using the paste is a wiser choice.
Thanks again,
Larry