I've never found the MRM 30 to be efficient. Why not bump them up to 3xMRM40? You could bring a bigger engine with the tonnage you save. If you're chainfiring, then it's much cooler than the MRM 30 model. If you alpha strike, you get 5.23 ghost heat, which may seem like alot, but it's only 39.73 total heat. Chain firing four MRM 30 gives you 38 heat, and alpha striking with 4xMRM30 gives you 45.98 heat. With 13 heatsinks on the MRM40 version, it's probably cooler alpha striking even with that ghost heat than the 11 heat sink MRM30 version would be chainfiring!