Not clear. I seem to remember reading of a stronger fentanyl derivative within the last month or so, but can't immediately find the reference.

If you're interested in the status of fentanyl and its derivatives, as well as the directions being explored for their pharmaceutical use, here's a well-written, chemistry-heavy article [1]. Not paywalled.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4137794/pdf/nih...

Yes, lofentanil is slightly stronger.