Carrameow: Based upon the factors you listed, I think you answered your own question. Also, I agree with Larry that you should wrench on stuff you enjoy the most. In my case, for some reason, MB designs make the most sense to me, so it's easier for me to learn about them than with other makes. I like their elegance and simplicity of design.
However, if the high speed performance factor matters to you, there is merit to looking into either a Porsche or a BMW. Neither make, to my way of thinking, seems to have the same long-term build quality as a Benz. But taking driving skill (or lack of it) out of the equation, if I were able to drive two cars at the same time on the same stretch of twisties on Highway 1 along the NorCal Coast, no stock W124 I've ever driven would be able to keep pace with my other me driving a same-year stock 5-Series, and no C-Class could keep pace with my other me driving a 328is. Porsches are apples to this comparison of oranges. As I've said before on this forum, I think the Benz offers the best compromise of quality, performance, utility, engineering and longevity of any marque. They are the best "balanced" cars made. For that reason and because I'll probably always just own one car at at time, I hope to always own a Benz. If I become insanely rich (according to my standards) and could spend the money, I'd have 2, and the second would be rip-roaring fast, fun and non-utilitarian. And it would be sexy and happy going topless.
2003 Dodge Durango SLT
2002 BMW E39 530i Sport
1988 Mercedes 300TE
2003 Chevrolet Suburban