From experience: the P7 sliding dropouts are fatally flawed and will fail you repeatedly, finally dumping you with a load of heavy metal that a moment ago was a rideable bike and is now just a load of metal- in the middle of nowhere. Cue Deliverance scenario.
Buy an On-One "proper sliding dropouts that work" Inbred…
…Except you can't cos they don't do them any more (they do horizontal dropout bikes AFAIK).
Ah-ha! But I have an original white DN6 (ie steel) slidey that is for sale with SS and geared dropouts.
A very very fine bike for sale, I may break it if you're polite.
Might suit you?
al.