The HD1000 manual says to use a card that's rated for at least 3MB/sec.
Yeah, you'll need someone fro Roku directly to tell you if the hardware itself is capable of taking advantage of a high speed CF card. Hope you get an answer, it's something that OUGHT to be in the FAQ.
HD-1500 RevB #1 (media room)
Mitsubishi WD-62528 62" LCD RPTV
Kenwood VR-407 receiver w/PSB Alpha's
PS/3 60GB (now 250GB) w/750GB Seagate ext
HD-1000 RevB #2 (bedroom)
Visco 32" LCD
AR 2.1 audio system