Upload & Sell: On
Jim, the size! and I have 70-200 f4,--that I can't do without--, and with 400mm prime, I can add on tc(s) that will have a decent IQ.
With the 80-400 the 70-200/4.0 is less important. The reviews I read say it's a great lens at almost the whole FL.
Weight is a little more than the Canon 400, but much less than both. No lens change necessary.
I would say the 80-400 is less bulky (at least to transport). Filter size is 77mm for both.
Only big difference is price, but it will come down after a couple of months.