I just bought a Giant OCR3 from Wiggle for £425. It's reasonably
light, everything is comfortable and I am averaging 15-20% faster than
on my MTB. I have also discovered that going up hills is kind of fun.
Not complete fun, but more than on my MTB. I have also learnt that I am
not Lance Armstrong, but occasionally deluding myself is fine. Just be
careful not to have someone fly past you in the middle of this
daydream. I've had quite a few "nice bike" comments, one from Dr Bike,
others from other complete strangers. They've been amazed you can get a
nice bike for that price, and you could see their brains working
overtime trying to figure out how to explain to the wife

I am averaging about 16mph, so you should be in work within 20-25
minutes depending on how much downhill it is

Finally, a friend had his £2k Trek race bike the other day and feels
like a feather compared to mine.