E63 630i bj. 2008 or E63 650i bj. 2006 with SMG

Hi guys, I’d like to get a 6er and found two interesting vehicles, but the decision is not easy for me. However, I have to consider the 650i a bit, because so many warn of the known problems with the valve shaft seals and the water pipe. In addition, there is the opinion about SMG, which should also be problematic. The 630i is the facelift model with 272 HP, which should have some problems with the injectors. I ch knows that these topics have been addressed many times in other threads, but I would like to hear your opinion in the direct comparison of the two above mentioned models. Perhaps one of you has had experience with both models. I personally tend to V8, because it is a V8 mega power and sound. But I am afraid because of the possible costs that might come on one regarding repair, since after the purchase for such things would be for the first time max. 1.500 euros left. Ps. rides a lot short distance and In addition, I would like to know how it is with a child seat in the back, because of my 2 year old daughter, because I also want to take longer family trips with the vehicle.