Devils's Canyon is not a new architecture. Devils canyon cpu's are haswell cpu's with a next generation thermal conductor instead of regular thermal paste on older haswells between die and ihs.
Also, the I5 4670k turbo's to 3.8ghz.
After all, the difference is minimal. If you only want to oc to ~4.2ghz, go with the cheaper one. For running on stock or oc'ing higher, the little extra is worth it.