PSM also claim to have actually played the played the game which could mean that many other magazines are also getting similar previews. Finally, they say that the only loading times are starting up (obviously) and travelling between islands.
"This weather effect is actually new to the GTA universe, not just Liberty City. The one thing to keep in mind is that it will actually affect the driving physics, as the roads become more slippery."
PSM Issue 102 goes on sale early Sepetember
Thanks to GTAPSP for the heads up.