Klippan Century is the rear facing one with the tallest harness. It can accommodate up to approx 135cm. In fact the i-size version, Klippan Opti, which is approved to 32kg (but only 125cm!) has been crash tested with the Q10 dummy which is based on a 10yo and is about 133cm tall. You can see the video on the web, I'll link it if you want.
Joie Bold is the forward facing one with the tallest harness. You need top tether for it. The crash test results are only average, although this is typical for 25kg forward facing seats.
Unfortunately you can't get 25kg ERF seats which convert to HBB, but I don't usually like HBB seats bundled into harnessed seats anyway. In general, get a harnessed seat and then get a booster seat, and let each excel at its own job rather than having to compensate for being able to do the other, if that makes sense. The only time it makes sense to buy a harness/booster combo is when you have a child who only needs to use the harness for a short time and it doesn't make economic sense to purchase a purely harnessed seat for them, but they are still too young to be safe/responsible in a booster seat.
Joie Stages does have a slightly taller harness height than most 18kg seats, and Cybex Sirona is a particularly short one (hardly any children get much past 3 in it, let alone 4!) but you might find the Stages annoying to use after using the Sirona. It also isn't quite as roomy as a 25kg seat simply because it's a very different type of seat, it's more reclined. It's also not quite as tall as most 25kg seats, even though it's approved up to 25kg as a booster seat. I don't have experience of comparing the two side by side, but I have been assured from people who have, that it's not really comparable - you do get more space in e.g. Axkid Move, than Joie Stages.
The annoying things about it are the one recline position, the way the belt is always in the way, the amount of room it takes up in the car.
The Joie Every Stage has an even taller harness, in theory you can extend it right up to the top height when the seat is used as a booster - this differs from most 123 seats, where you usually have to detach or stow the harness at a certain point before the headrest can be raised any further in booster mode. However the crash test results for the Joie Every Stage are not great, even in rear facing mode. (It also has the same downsides as the Stages). Personally unless you're really stuck for cash or looking for a travel seat, I wouldn't usually recommend the Joie belted range for rear facing. You're almost always better off with a 25kg rear facing seat, even if you don't need the weight capacity, just the height.