I played around in 1.7 for a while and the inital chunk loading stage was very laggy, but quitting and restarting the world seemed to help. And after that, it actually performs a lot better than 1.6, for me anyway. Next time I boot it up I will make sure to disable Botania because those flowers spammed all over the place with their little particle effects just cant be good for framerates.
I use the following settings:
# The density of each flower patch generataed, defaults to 32, the lower the number, the less each patch will have.
I:worldgen.flower.density=4
# The quanity of flower patches to generate in the world, defaults to 3, the lower the number the less patches geenrate.
I:worldgen.flower.quantity=3
Seems to generate sufficient flowers. Haven't actually used Botania yet, so might be too much of a "nerf", but the world looks so much better without the flower spam.
Also, disable any "shedding" in the config. That's just another massive amount of entities floating around and extra processing.