Neither speed nor size is important if it does not reflect agility and power. There are lots of track athletes that have sub 4.4 40ties out of pads that are football slow, yet others who 4.6 40ties that play fast because they can run that in pads and come out of a football stance at full speed.
A weight difference is only of significance when it is massive across the board. Yes a team with 260 pound tackles and 220 pound ends will get eaten alive.
The other item to be aware of is scheme. A zone blocking Oline does not have to be big. I am going by memory but I believe the Bronco's Oline that won 2 SB's in Elway's last 2 years were the smallest in all of professional football. The same with some spread & shred. The classic spread & shred is to pull an athletic guard or center and isolate on a hapless linebacker. Converse to power like Wisc you put a premium on road graders. This what UM is trying to do. Last year UM tried to zone block and it was horrible. Big guys were no good.
Another example is a comparison of Mo Hurst to Brian Mone. Hurst is 290 pounds but much more explosive. Mone is a real 340 pounds and probably the strongest man on the team. Yet it was Hurst who played NT and who would have been a first day draft pick if it were not for a heart condition. The power that Hurst generates plus the speed to bring it was more valuable than Mone as an immovable rock. You can always run around Mone and Hurst gets to the QB faster. So the little guy even if got run down a bit because of no backup did pretty good yet the big guy had problems other than goal line situations being an effective tackle despite the need for one.
So speed and size can sometimes be over rated. Football players end up beating those who are just big, fast, or both.