The Type 45 can turn pretty handily even whilst flat out, in trials Daring actually performed better than they thought she would in this and most other respects. In fact, there was an incident during a PR and media event when during one such turn, some unsecured camera equipment ended up going overboard. They've actually been built extra wide to accommodate the top heavy structure with adequate stability, which is part of the reason they're so large both inside and out.
As far as stealth goes, the Type 45 has been designed from the ground up to have a lower radar cross section, as have most modern warships (Horizon and La Feyette spring to mind), even the Type 23 frigates were designed to be slightly 'stealthy', although not to the same extent. Even so, the idea of a 'stealth' ship is a misnomer, as no matter how uncluttered a deck or angled structure you have, a 7,000 tonne warship will still show up as a large return on a modern radar. As with airplanes, all 'stealth' does is reduce the range at which you'll be detected, which with ships doesn't make a whole lot of difference when you'll still be detected over the horizon anyway.