Yes Daniel, if you play Minecraft Singleplayer it will create automaticly a local Server, and this needs more CPU and RAM Resources. So the Mods need more Resources too. So you need the Power to handle those things in the Same time. I tried the Modpack on my WindowsXP with 1280MB max amount of Ram and it worked fine. (I install the Mods Manuel with Forge). I’m using Windows XP for fun and loves it 😀
I have 15 GB of ram singed to minecraft and on ftb unstable with few additional mods i have 200 fps max, but i locked it on 120 to make it stable. I’m still far from late game stuff so my fps may be lower later.
I also use 6GB for this pack in single player. Keep in mind that more is not always better. Allocating too much RAM can actually cause lag spikes, because Java will do garbage collection less frequently, and therefore will do more garbage collection each time. Also, you usually don’t want to go much more than 1/2 of your physical RAM, as doing so can cause frequent memory paging (swapping of data between RAM chips and hard drive).
I plan on posting a video soon going through my video and RAM settings for Minecraft and other optimization tips. Feel free to add any tips you think I should include.