Paint for cast iron gutters - Hammerite smooth?

I've recently replaced the one 6m length of PVC gutter bodge on the house with cast iron to match everything else (a slightly tough job, single handed; where are the off-spring when you need them?) The new stuff was pre-painted and looks great, but it's reminded me how bad the rest of the guttering looks (in good condition, but bad paint and with leaking joints). The plan is to take it down in sections, wire brush, paint, re-fit with new bolts and seals, and to adjust the brackets to improve the falls. The question is what to paint it with. My first thought was inside and outside with Hammerite smooth, but I've read reviews saying that it flakes quickly and is a pain to apply ("not as good as it used to be"). Other suggestions are to use bitumen paint inside and almost anything outside. Any recommendations from people who have relevant experience?