Having spent the last few weeks looking at a variety of Golf GTi Mk5's I'd say you could reasonably ask £10.5k but you'd get a lot more interest if you could drop below the psychological £10k barrier (say £9,995)
Enthusiasts may pay a bit more for the right car but most punters don't care. Spec seems to be important so the more toys it has the better and for some reason 5dr cars seem to hold there value better (for practicality reasons I suppose, as I think the 3dr looks better)
The cheapest ones go for a shade under £9k but these tend to be leggier examples ( I did see one for £8.2k but it had done +130k!)
My budget was 8k tops so irritatingly I couldn't quite stretch to an ED30, so in the end I got a standard well specced GTi and got a bluefin
Hope that helps
Paul