What are you hoping to use it for Dec? Mostly aviation photography nd if so, mostly at the airport, e.g. BHD, DUB, or mostly for contrail photographing?
I find myself constantly at 400mm on my Canon 100-400mm so I'd be a fan of the 150-500mm. I do like close up shots of aircraft although sometimes I can't even fit an aircraft into the frame side on at 100mm. I can't comment on quality of either lens but I imagine they'd be relatively close.
Dave