I mainly train and run in 5ks and 10ks. My 5k Pr is 16:43 and my 10k PR is 34:54. I run a long run of 14 to 16 miles about every two. Would I be able to run a half way decent marathon in 5 weeks without injuring myself and without hitting the wall in the last 6 miles? My average MPW for the last 12 weeks is 67.8 MPW with a high of 80.