Hurri/Spit, both have the Merlin, so why is the hurri so much slower?

[Soviet Ace]

Just like the Merlin with it's different versions, the DB601-605 had their own versions as well. That's why there's different speeds etc. for certain 109s, that were powered by either a 601 or 605. I mean a early 109 powered by a 601, and a later 109 powered with the 601 as well, will more than likely have different speeds because they did this and that to increase the power of the 601 or 605.