If the only reason you're moving to reta is fear of missing out, I'd stay with tirz since it was already doing what you wanted. Is there another motive for the change, like wanting the glucagon action? I'd avoid pushing the reta dose higher right now because any sides that show up could land hard.
I've been using tirz since late June of last year and added a small amount of survo on top starting around November or December mainly to ease fatigue, though I don't plan to keep the survo once I reach maintenance. I've dropped nearly all the extra weight and am nearing the finish line. I have a large supply of high-dose tirz stored away and have mostly stopped worrying about running out. I began setting aside some reta without any plan to use it soon because I prefer waiting for more real-world data on newer meds, but I thought I should test it for a few months now so I know how it sits with me before committing later. My plan is to taper back down afterward and return to tirz for the time being.