It depends on how good a gfx card you have.
In production, we don't use the viewport for trees, we use points or outlines, or nothing, to keep viewport fast.
This way you can instance 125,000 times larger amount than you need with 200 ( 25 million trees ) and have 100fps in viewport.
We use the Arnold IPR render view to look at the trees which can work with much larger amounts.
The only reason to see the trees in the viewport is because you need to simulate, or do something concrete with some of the trees, else they just stand still or animate and in that case, there is no reason to see the trees in the viewport.
I'm not seing any real slow down with 200 instances of an .ass tree ( 45 mb ) set to bounding box.
Maybe your gfx card is not so good.