I was thinking about trying TE4 sometime soon, until I discovered in the documentation that some of the late-game materials rely on drops from hostile mobs added by the mod (or possibly by one of the related mods, like Thermal Foundation; close enough).
IC2 seems better in this regard, since afaik the only two hostile mob drops required for its recipes are gunpowder (for extracting sulfur from for making advanced RE batteries, if I don't have another mod such as Railcraft to get sulfur from) and bonemeal for making fertilizer (though fertilizer can also be obtained as a fermenter byproduct). Technically, both bones and gunpowder can also be obtained from worldgen treasure chests, and as far as I can tell, neither advanced RE batteries nor fertilizer are strictly required for progression in the mod.
Now I'm wondering which other tech mods work well with Peaceful difficulty, and which rely on hostile mob drops for progression. I know there's the Peaceful Table from Extra Utilities (at least in 1.7.10) as somewhat of a workaround, but I've been unsuccessful at determining whether it's limited to vanilla hostile mob drops.
Also, before somebody suggests asking this at the Minecraft Forum site, I'm currently unable to post there (where the reply area would normally be, it just says "Loading editor...") I have contacted support about it, but they weren't much help, and I can't even tell if they got my email reply to their message asking for more details.