Am desperate for a glidey, light, quite fast bike. I do a daily commute of about 4 miles each way, mostly pretty flat with a few slightly uphill bits, and am about to start a new job that will involve quite a bit of gadding about by bike. :):):) Currently have heavy clunky v slow decathlon bike and it feels like I'm peddling through custard. I can spend about £500. Any recommendations? What do people think of this?