My daughter used a booster (very) part-time from 4yo+ (she was 43ish inches and 44ish pounds at that point), but she didn't move to a booster full-time until right around her 6th birthday, about 49-50 inches and 50ish pounds.
She was 40 pounds at 3yo, and we got a Britax Husky (precursor to Regent). It didn't install well in our new (to us) vehicle, so we had to sell it when she was 4. We tried a Britax Parkway as a full-time seat at that point, but she was in no way mature enough to use a booster full-time. We got a discontinued) Fisher Price Futura to re-harness her when she was 4.5. When she outgrew that we had yet another vehicle, and got another Husky. She used that until she turned 6, and we felt she was mature enough for a booster full-time.
My dd has always been in the 95th+ percentile for height (since 9 months old), and the 80th+ for weight. Had she been more average, and had they been on the market at the time, I'd have gone with a Graco Nautilus or Britax Frontier over the Husky/Regent. Really, the Nautilus/Frontier would have worked well even as big as my dd is; she would have fit in those (harnessed) to age 6. She's 7.5 now and probably right at/slightly over the Regent's top slots. At one point in her life (ages 2-4) she was all torso, then her legs caught up and I feel she's pretty evenly proportioned now, for her overall height (19.25 inch torso, stats in signature are current).