Torn between 70-200 F4 IS and 135 F2

Hello,

I have a Canon 7D.

I'm doing mostly portrait, conceptual and details work. I currently use 50 f1.4 and Tamron 17-50 f2.8 and love them both. However I'm totally in love with 50 f1.4 and the quality I get when I use that lens.

My portraits are usually headshots or head and shoulders (kids & grownups) with very shallow depth of field. The 50mm (80mm on a crop) is really the minimum I could use. Too often I find myself too close to the subjects. I love isolating them with shallow dof and going "in your face".

I thought about adding another lens to my small but trusty arsenal, to get more reach. I thought about 70-200 f2.8 non-is. However, I questioned the quality, the price AND the weight. Not for me.

I fell in love with 135 f2. The creamy yummy bokeh, large aperture, sharpness, contrast... perfect. I was blown away.

The downside is the focal length on the crop - 216mm. I do work in the field a lot, so that's a plus, but I guess I would struggle to use it indoors (or maybe I would just switch to 50mm?). However, I do plan to move to the full frame soon (next year or so). So I know that 135 on FF will be JUST right for me there.

Then I thought about 70-200 f4 IS and the versatility of that lens. I won't talk about it here, it's a well known, excellent piece of glass, but f4 isn't that large and fast. Since I photograph mostly people and something that relates to them, IS is not something that I would benefit from...

I really like using large apertures and isolation it produces, even on the good light... it's just that 70-200 seems more versatile, "indoor work"-friendly and more bang for the buck (they are both similarly priced). Yet with 135 I will definitely have to be more focused on what I try to achieve and that can be a good thing.

What's your word about this?
Thank you!