So is it safe to say that a Techmarine may well be the most badassed member of a Space Marine chapter. Better than even Terminators?
I don't know. Being fully upgraded would boost them beyond the superhuman level of regular marines. But at the same time they'd be losing a lot of things that the flesh has an edge over machinery. Such as being able to touch and feel, taste and smell. By losing more of their humanity it might lower certain capabilities of the marine. And then there is the psychological aspect. I'd imagine when you're more of a machine than man you'll be in a completely different frame of mind. Your mind will work like a computer analyzing everything. You may be less or more prone to taking risks. And you may well lack the compassion and fellowship that allows you to fight alongside your brothers. So you may be less apt to aid a brother in need during the middle of a fight.