The carrera has 9 speed rather than 8 speed rear gears, its nice but not necessary.
IMHO ..
Both bikes have alloy forks when for the same money you can get bikes with carbon forks and better gear but i was tied to
halfords C2W like you and i went for a boardman as they always get very good reviews in the cycling press and offer good value for money .
Can you stretch your budget to £650 ? it will only be a few more pounds a month and you can get the boardman road race which has a better frame , carbon fork and mavic wheels.This is a good bike and very good spec for the money .I have the road comp with sram apex which is a fantastic bike for the money but its currently on for £799.
Another option is to ring up the halfords C2W as they can source non halfords bikes from the major manufacturers but you will be looking at full rrp .I nearly bought a cannondale synapse but the boardman offered the most bang for the buck.
I actually ride a virtuoso for commuting /winter club runs and its been a solid , dependable bike that i still get pleasure riding .It might be a bit heavier than my nice bike but in the real world your average speed is not going to be that much faster , just smoother and a bit easier to climb on.
