a nice subject for a new lens, Kevin. When I got my new 85 f1.8 lens I could not find anything nearly as good for 4 days.
ah that makes more sense !! tripod and gimbal for one of those there are some tripods that have the option to convert to a mono pod via one leg coming off and attaching it to the head direct my benro classic has that feature, get a carbon fiber one, i was walking around with mine the other day and forgot i had it quite literally.
Kevin do you have a shoulder strap like the black rapid for the big lens? i found that to be really useful on walk around without a tripod, i found just the carrying without a strap beat my arm up alot that when it came to shooting i felt it, with the strap hand held was alot easier. a polyfilled bean bag will weight nothing but give good support if you have somewhere to rest it
have you got any extension tubes you can try with the 150-600 kevin, you will loose on the long end but you will be able to get alot closer to close up subjects, i found that was a good option than taking two lenses out
i very strongly recommend you get a good brand of tube if using them with the heavier lenses, i have had a neewer one snap under the weight of a 100-400 with a x2 converter. i only trust canon ones for heavy / expensive lenses. i mention it as its not something i thought about with tubes, i got luck mine snapped while on the table