Motivated by these posts, [An NP-complete variant of factoring][1] and [Relationship between symmetry and computational intractability][2], It seems to be worthwhile to investigate the different factors that increase the hardness of problems in NPI. I'm interested in other NP-complete variants of problems of intermediate complexity. Is there a recent survey paper of $NP$-complete variants of problems of intermediate complexity (problems between P and NP-complete)? Cross posted on [TCS StackExchange][3] UPDATE: Bounty may be awarded to an answer that gives other interesting NPI problems that have an $NP$-complete variant. [1]: http://cstheory.stackexchange.com/q/4769/495 [2]: http://cstheory.stackexchange.com/q/871/495 [3]: http://cstheory.stackexchange.com/questions/6761/np-complete-variants-of-npi-problems