Don't like that one bit. No reason your speed should decrease at all. That's quite different from other people's experience comparing CloudFlare to CloudFront. If you have a second, submit a ticket and we'll make sure you've got everything setup for maximum performance.
Thanks for your concern Matthew, I'm not very worried about this. That 13% of difference in speed is most probably due to the fact that Amazon has a Cloudfront edge location in Madrid, the city most of my traffic comes from.
I haven't really measured the speed from other locations but I will do it and file the ticket to let you know about it.