512mb/s would be fine - best with a 1 meg + service though.
I've done alot of switching ISP's. Firstly, stay away from Tiscali like the plague. Seriously, do not even think of going with them. Customer support - crap, speed - crap, latency - crap. Freedom 2 Surf are good, I'm with them now.
You should check out
ThinkBroadband. Its got speed tests, ISP reviews and best of all when you do a speedtest, it takes your ISP details etc - then puts them all up into monthly totals. Its great to compare ISP's when you're changing.
If anyone needs any advice on switching just ask.