It's interesting you say that. I am on a potato PC: 2007 quad core Intel CPU and a 2011 560Ti with 8GB RAM. In 1.0.5 and earlier I had a lot of mods, say 100-120 and the game ran surprisingly well. It was only when part count started rising or I tried building space stations that things got rough. I use Linux so had 64bit for ages.
I assumed that with the upgrade to Unity 5, improved and more efficient GUI and better multithreading I would see better performance but even at just 80 mods the game is unplayable. The space centre itself lags badly and loading into the VAB lets me go make a coffee and often just crashes.
Quite disappointing as I am now far more restricted in playing the game. I think I'll have to downgrade to 1.0.5 and stay with that till the latest build improves or I upgrade my PC, hopefully later this year.