Significantly faster based on what? Cu is directly compared to both lightning and light with regards to his speed and even his afterimages have afterimages, so they can't even go there with regards to Soi Fon's afterimages.
Nevermind the fact the dude went TWELVE HOURS with Gilgamesh before going down. Soi Fon would have lasted SECONDS and even that might be generous.
Nah spacebattles-san, Soi Fon WILL die when that lance is thrust.
It's worse when you get out of F/SN and go towards how he's treated in the other series:
Fate/Extella: Kills Jeanne D'Arc(Who is able to handle Casual Island Attacks minimum from a nearly Critical Spartacus) and wants his rematch with Gilgamesh. Otherwise seen as the fastest in the Moon Cell and one of the strongest around
Fate/Extella Link: Hilariously clarifies that he's a Candidate for Top Lancer(i.e. one of the designations of being a Servant capable of protecting the Moon Cell) with KARNA and only lost it to Scathath because she legit "cheated" and is a virtual Immortal.
Fate/Grand Order: His Alter Cu-Alter is capable of defeating multiple High and Top Tier Servants with only the help of having a Master and some Shadow Servants.
Soi-Fon ain't doing shit.