Wait how does sPvP put the same amount of strain on framerates as a city? I thought the most you could have was 8v8?
My FPS during sPvP was probably averaging around 80-100, 60-70 if the shit really hit the fan with most of both teams in the same area throwing spells. The maps are generally far more confined and smaller, you should be getting more around the same fps as quest zones (or higher). In WvW I come down to around 35-40 fps.