the reason for your FPS drop is that SR1 has set default FPS of the game at any time 15 min to 30 max. this is why you will not have 60 anymore.
But then, your eye cannot receive images at 60/min either, so you lose nothing, you gain smooth game.
Try different heapmode - for me best is 1, for other players - 3 or 5.
As for Streamline, yes, IMHO it is a must, just you have to make some changes after reading the readme.
I play at 11 trees visible with the correct fog settings and some other adjustments, like setting the FPS range 15 to 30 as SR1's.
There is no current mod that can beat streamline in what it does - it still does it best.