It's not terribly off, 35 det = 4.865 str per the stat weights.. But regardless.

Skill speed has more value at low levels and lower value at high levels. It's all situational. In my situation I wouldn't wear gordian boots until I could drop skill speed elsewhere, as far as I've been able to tell, running with different sets at 600, 640, and 690 numbers, there's not anything I can do at 697 I couldn't do at 647, and certainly nothing I need 747 to do. If you are talking about going from 550 to 600, or 600 to 650, then there are significant benefits that you can see.

And maybe that's the kicker. The negatives of higher skill speed are more noticeable than the benefits. It's easier to see that higher skill speed is disrupting double-weaving and nearly throwing BotD to after CT/FT instead of right before. Whereas, it's not incredibly obvious when you get an extra hit that you might not have gotten at lower levels.