Two reasons for sticking with the 7805 approach. The first is that the 7805 is virtually free compared to any of the intergrated switchers and much easier to find as well. It isn't nearly as elegant or satisfying technically but who is going to see it? An extra watt in a car is easily provided and easily dissapated. I don't think any part of my 7805/SV6 is over 45 degrees C.

The other reason is that you are dealing with a radio receiver designed to recover a signal that is nominally -130 dbm at the antenna. We are talking about something that is well below the ambient noise level. GPS only works because of the spread spectrum, synchronous detection architecture. It doesn't take much noise to start to degrade the sensitivity of your preamp and switchers are clearly much noisier than three terminal series pass regulators.

If you do go the switcher route be careful with grounds and shielding. If you keep the radiated noise of the switcher and its external components (particularly the inductors and any schottky diodes) bottled up you can certainly make it work.

Lynn