Now, this mod is a bit tricky to use, but once you can, it'll be agreeable ;) I call it "archangel" because I use it in combination with a pistol I modded to invisible blasts of power. The mod you can download here will reduce the effects of gravity while jumping, making you levitate, and allowing you during that time to move around at an enormous, nearly unbearable speed!

 It's a new player.bin file you can extract to your dropzone folder. By jumping, you'll levitate and climb slowly up to 30m; it will then go into free-fall mode. I did this by switching the "gravity" value at the bottom of the player.xml up to 0.4 It will, thus, make you climb but not too much. Now, the "9999" value right below the gravity value means you can move around, while levitating (that is, in the timeframe needed to reach the height of 30m). The thumbs I added show you that a distance of 12 km / 8 miles has been crossed in less than 1.5 seconds! We're talking Mach 15-20 here.

 The best use I can find is starting at sea-level, or better, at the sea, since you may accidentally land on solid ground that would be in your way and you will hardly cross a boat offshore. It's not as fun as flying (and I recommand you download the Superman-mod), but if you wanna be on the other side of the archipelago in less than four seconds, you'll find it fun.

Moreover, just jumping without moving (or moving too much, remember, you're fast!) makes you levitate and thus able to shoot at everything as long as you're not over 31m over the ground (which will make you free-falll).