Have you check this lens from Sigma? It's not the cheapest one but it's worthe the price from my point of view:
Sigma 150-600mm f5.0-6.3 DG OS HSM Contemporary
I was looking at it last year, but also was looking at Canon 100-400 IS L too.
I think upgrading your equipment is really expensive. I don't think I will be able to afford it.