Change convector radiators to cast iron?

After having a new oil-fired hot water boiler installed, Iím considering the value in replacing some of my convector radiators with cast-iron. But, not sure if it's worth the hassle. Which would feel more comfortable and/or be cheaper to run in the long run? For example, convectors require shorter more frequent boiler firings to keep the temp steady in the house. And although cast-iron radiators require longer boiler firing time to heat up, they stay hot longer. Sounds like itís an even wash either way, but your comments are appreciated.
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