1x CD is 150KB/s so 50x would be 7.5MB/s, USB 2.0 is 480(?) Mb/s or 60MB/s. Putting overhead aside and assume the flash can reach that speed, yes. However, none of the off-the-shelf flash can have that speed. It would be at best comparable but I guess in general slower if the claim of 48x CD is real(that I have no idea).

BTW, I am thinking along the same line but instead of 1GB, I am aiming at the 256M CF which is very cheap nowadays. A trim down KNOPPIX can fit into it and there would still be some space for persistent home. The only problem is machine supporting USB booting is still not the majority.