If you are using Forestry's Multifarm instead of MFR's Planter+Harvester, it should not be laggy at all.
A full 36 blocks (exclusing the firebox) high pressure steam boiler can provide up to 144 mj/t (18 Industrial Steam Engines).
Few ways of feeding it, my favourite is running two 9x9 MFR planter+harvester tree farm (oak if vanilla, sakura/magic tree if BoP), running the wood blocks through an induction furnace (while I was still playing with ic2) to turn them into charcoal before feeding them into the boiler. But not efficient, works though.
Another way is to just feed planks to it, seems like that is the most efficient way. Or maybe only if you're using a sawmill to yield 6 planks per wood block.
If you want to run on MFR's biofuel, you can maybe run multiple tree farms as well. Feed all those excess saplings to the bioreactor for biofuel, and the more kinds of saplings you feed it, the higher the efficiency rate is. The bioreactor also accept all sorts of plantable stuffs like seeds (all kinds), netherwarts, carrots and potatoes.
Or of course, more solar panels.
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