the second is faster since it has faster clock speeds.
neither of them need an external power connector.
you only need an extra power connector if the card draws more than 75 watts and nothing under £150 is likely to need the extra power - but if you have any half decent psu it wouldnt be a problem anyway.
if you can spare an extra 20 quid then go for http://www.scan.co.uk/Products/Produ...oductID=364487
its a 7600GT and will give fantastic performance for that price. The x1600 is fine for now but the 7600gt is a lot better.