Planet X Pro Carbon Track?

I've been looking at buying a second hand track bike for racing, mainly for use at Herne Hill (but want to have the option to branch out to Lee Valley etc). I've found a lot of Planet X Pro Carbon track frames out there, and wanted to know people's opinions on them, as I can't find many reviews online. Obviously they're fairly cheap compared to some higher end carbon frames, and also older. Want to know what people think about them, specifically about their stiffness and sizes:

• I've heard from some people they're pretty flexy: is this true? I'm hoping to race on it competitively, so want something stiffer for the high end power sprints.
  
• I'm about 80 kg and 189 cm, would the size large frame be suitable (their biggest one)? Its reach is only 20 cm longer than my roadbike's, compared to a Dolan DF4 59 cm where the reach is 50 cm more. I'm worried that as I race more I'm going to want to stretch out my reach, and might be limited
  
• Anyone got any other opinions/experience on them, and if they're good value
  
• Or can anyone suggest any alternatives?
  
  

I quite like how they look too, which obviously helps