Some of the best and most memorable fights I've had in EVE were as an RP with RPers, but generally because RPers fight differently in a sense.
Two sweeping generalizations about RPers that I find to be mostly true, but will rub some people the wrong way.
1) In general, RPers don't like actually fighting in space all that much with other RP entities--it's harder to control the "story" so to speak, and invariably one side finds itself at a very lopsided in-space disadvantage be it due to numbers, skill, resources, what-have-you, when "IC" no such disadvantage or no reason for said disadvantage exists. And many RP entities aren't primarily PvP entities, despite their RP, and as such tend to get kicked around by more PvP-centric entities, be they RP or not.
2) When RPers do fight, contrary to what one might think, it's generally not a purse fight. In my experience fighting RPers with SF and later STIM, when an RP group decides to fight they fight until their last man (incidentally, this tends to end with their group ground to dust in cases where they are at a disadvantage, and this contributes back to #1). Aegis Militia was that way when we fought them as SF--no matter that they lost just about every fight we had with them, they kept coming back every night for another fight. Same can be said for Acheron when we fought them as STIM. I think they mustered less than 5 kills on us in the war we fought against them, but they came out swinging all the time. And some of the best fights to the death were RP-related. CVA vs UK+SF in Amarr comes to mind. I feel like it was 30-50 vs 30-50, mostly BS, and it was straight-up a slugfest that went until one side had nothing left on the field. Both sides had something to prove, and left it all on the field rather than running when things looked like they weren't going to go their way.
That said, those generalizations are based on my experience fighting RPers as a member of SF and later STIM, and may not reflect the experiences of most. And many RP entities don't fit that mold. Many of them are indistinguishable from your typical napfest nullsec alliances (no offense Mammal, but you guys are in that category with your NCBFF affiliations and previous Proviblob affiliations). I don't even count those as RPers from a PvP perspective, because no matter what you do to try and engage them in a strictly RP fight (ie, RP entity vs RP entity), they fall back on their allies and space.
Again, all sweeping generalizations, but I find for the most part that these are true when it comes to my experience.