First let me welcome you to Aximsite
Yes you can have both an SD and a CF in and working at the same time however if it comes to a choice between the two, you should go with SD and leave the CF free for other accessories such as a CF camera or a CF FM radio. There are more of these accessories in CF than in SD format.
BTW I'm guessing "chuffed" is a good thing, I've never heard that word.
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Give a man a fish and you feed him for a day. Teach a man to fish and he'll be gone all day.
Traffic lights that are set for 35 are also set for 70