I really like Big Reactors and the concept is fun, but i feel you can get them too early. I opened a single player world and rushed straight past other power methods and got a 5x5 setup in about 3 hours. So maybe to push it back a little bit, As i think reactors should be a mid/late game item. Put in the config an option to replace use of iron, with use of steel. This would push back the reactor and require you to actually do something prior to making a reactor

This setting already exists. It's called "requireSteelInsteadOfIron".

See the BR config documentation here: http://wiki.technicpack.net/Big_Reactors_Configuration