Ouch, I recently did this - well I had the 135, bought the 70-200, realized I wasn't using the 135 much anymore, sold it for a 300 f/2.8 IS II. It was more sacrifice than sacrilege on my part, and I'm sure I will miss it at some point
I would replace the 135f2 with the 70-200 2.8L IS II, but otherwise a golden rule, yes
I do wonder how this post could keep going for all of these pages. The 85 vs 135 decision is an easy one
You sold your 135 for a 300 f/2.8 IS II? Hey, I'll trade you even for mine, if you want to get another 135mm :-D!
No, I was extra
sacrilegious - I sold my 35 1.4, 50 1.2, 135 2, 400 5.6, Sigma 12-24, and some other stuff to fund it.
I loved my primes, and will miss them I'm sure, but between the changes in my commercial work (seeing less and less event work) and my happiness with the 24-70 II and 70-200 IS II, those lenses were collecting dust. I decided to sacrifice lenses that I rarely used for one lens I knew I would use all the time. Some sadness, but mostly glad I did it. I still have my 24 1.4 II and 85 1.2 II primes, which are the ones I still use a lot.
A happy side effect has also resulted from my smaller inventory of lenses (by some standards at least...). I don't sit around debating the prime vs. zoom argument each time I pack my bag anymore and I focus on using zooms for perspective and feet for framing