Welcome to BF! On that Chicago to LA run -- I'd definitely do it if I had only 8 days and the bike in question was a (large, "full dress" touring) motorcycle. If the bike was a bicycle, I wouldn't try that run if I had to average over 40 miles per day... and for us "ordinary mortals," I think that's a fairly aggressive level. Short answer: very unrealistic--don't even try it with that little time.