My first road bike was a 2006 Speedster S20, bought used in 2011. That bike got me into road cycling and I'd probably still be riding it if it hadn't been damaged in a crash. Most of my personal best times were on that bike (according to Strava). I did upgrade to an Addict a few years later when I found one on clearance. It would be hard to say it made me faster, and the Speedster might have been slightly more comfortable - the Addict is really stiff.

Based on my experience the Speedster is a great bike to get started on, and there's no reason to rush to upgrade.