Hey now... to save you some reading my understanding of the speed of the CF cards is that the slower ones have sustained continuous write speeds while the faster ones work in 'burst' mode. While burst mode is fine for cameras etc, it can get bogged down when alot of continuous data is thrown at it. When I had my Microtrack I was able to use the Kingston Elite 4gig and SansDisk ultra II 8gig line with no issues.
Stay Kind,
Dana