I got a tip recently from a professional about how to swing faster/hit ball further without extra effort. Take tennis ball and squeeze it often. This will make your hands and forearms strong so you swing easy with speed. Your winter golf gym must have more training. This one tip is easy to do, just I have not bring a tennis ball to office yet.
these guys swing feally fast, and pretty hard, there are 3 more if you like it, you can find them in related video.