> speed and severity of crashes correlation is quite established in literature, so I'm gonna wait for a study to come up with conclusive statistical data stating speed variance correlates more with injuries than absolute speed.
That is if a crash happens. If you compare crash rates and fatality rates on limited access highways where speeds are higher to other types of roads, you'll find that the former is lower on both counts.
> but you have truck and slow traffic on the highway anyway
Trucks do not drive that much slower than cars unless they're going uphill or have a speed limiter. With higher speed limits, slower traffic will most likely speed up to some extent and trucking companies may remove their limiters (or increase the speed where they kick in).
until then, it's conjecture, feelings and wishful thinking.
edit: then again urban and highway situations are different, so there's that. but you have truck and slow traffic on the highway anyway thus increasing car limit does increase speed variation in that situation and would be detrimental whether variance or absolute speed are considered