I would say upgrade. You get fitter by chasing and pushing at or above your level. If you always hang with the slow group you will never improve. After 9 more mass starts I will upgrade to Cat 4. I want to have clear goals. I have 1 race and 1 2nd (though doesn't really count, Greenbelt 'C' race) but still that in and of itself was a learning experience.
But anyway, upgrade. How else can you get better without pushing?