I know that Koukaku ghouls are generally slow due to their kagune being heavy hitting armor protruding from below their shoulder blade, but there are other things that factor into how fast a ghoul is, like lower body strength and stuff, right? So couldn't a Koukaku ghoul also be extremely fast? I mean, Kaneki had that heavy hitting centipede Half-Kakuja that was huge, and he was still so fast, he was running on the freaking ceiling! So I think it's possible if they were very strong, and if they had a pretty lightweight kagune, they could be fast, too. However, those are my thoughts on the matter and I would like a second opinion. Actually, it would really make me feel better if I got quite a few opinions on the matter, because I'm mostly going off speculation here.
I think it is just like you said, but this is just an opinion, as i couldn't find any information about this.
But if we take ghouls as humans, a little child would be slower than a man if both were walking with a 30kg backpack just because the man is stronger.
So a ghoul with koukaku should be able to increase is speed, to the point that would be considered fast, but it would be so much harder because it would not only take him to train his speed but also his strength and stamina.
PS: I consider this to be posible because there are no negative effects regarding to koukako (it is just heavy and extremely robust)