Virginia top speed is probably very close to value from RA (info from player who serve onboard real Virginia class) - i assume its less than 30 kts or not more than 30 kts.
Btw tiers table were made for RA 1.45 - not for real submarines
This is sensors comparison:
In my opinion Seawolf is much better than Virginia because have greater maximum and tactical speed and much greater firepower (and only noticable less sensitive sensors).