Having owned both there is absolutely no comparison the 16v is far superior. The performance just doesn't compare. I understand that they both use the same suspension setup but I'd have said that the 16v has a bit more grip when cornering, tends to understeer slightly less, but it does feel slightly lighter at the front when you get to 90+mph than the 8v did, not sure why that is, or maybe it's just my imagination.
I also get better fuel consumption with the 16v but that may be that I've slowed down considerably since writing the 8v off. 16v is quieter and has sound deadening under the bonnet that the 8v didn't, but the 8v had a nice little burble when it was sitting at idle that the 16v doesn't.
Both interiors were identical bar the fact that the first was a 5dr with aircon and the 16v is a 3dr without. I looked at loads both times round, wasn't bothere about special editions, or extras just wanted the best condition with most history I could find.
All in all, both great cars, but I'd recommend the 16v over the 8v any day of the week.
I'm dreading the summer, this is the first car I've ever had without aircon, think I'm going to melt, a sunroof just doesn't make up for it!