after a little googling i can find references to papers pblished in 1994 and 1995 that refer to GHz CMOS components (eg A. Rofougaran et al., A 1 GHz CMOS RF Front-end IC with Wide Dynamic Range, ESSCIR, 1995, pp. 250-253; J. Carols and M. S. J. Steyaert, A 1.5 GHz Highly Linear CMOS Down Conversion Mixer, IEEE Journal of Solid-State Circuits, Vol. 30, 1995, pp. 736-742.)

i know nothing about this, so perhaps they are irrelevant, but on face value it seems like a 2.5GHz system could have existed in labs at that date, or at least was clearly going to be possible.