Slic3r sometimes gets a bad rap here on the forum.
I found a trick in a book that increases slicing speed with Slic3r by orders of magnitude.
On the Slic3r “print” settings tab, uncheck the box “avoid crossing perimeters.” For objects with a large number of polygons this will speed up slicing from hours to minutes. You might also want to uncheck the box labeled “Detect Thin Walls.” This also speed up slicing.
For example, the “gyro cube” has thousands of polygons. By unchecking the box, the slicing speed changed from hours to two minutes on my computer! Also, if you have an i5 or an i7 processor with a lot of memory, change the number of Slic3r “threads” from 2 to 4. Modern PC’s have four to eight Gig of RAM memory and multiple core processors, so this dramatically improves slicing speed. If you have only a Gig of memory then this change can be counterproductive because it forces the use of the hard drive for “virtual” memory.
I’m using the latest version of Slic3r and find it to be very good. I’ve experimented with Cura but my opinion is that Slic3r is better and Cura has no speed disadvantage if you set up Slic3r correctly.
BTW, I abandoned the Velleman Host version of Repetier and downloaded the latest open source version which is bundled with both Slic3r and Cura latest versions. I had absolutely no problem changing from the Velleman Host version to the latest open source version. The Velleman version is OK for a newbie who wants to print something immediately after building the printer, but with a little experience you will want to switch because Velleman will always be months or years behind the latest version. In fact, Velleman Host has not been updated since March 2014 and I am writing this in mid November 2014.
There was a very small learning curve in switching from the Velleman Host to the latest open source version. Contrary to what I saw posted somewhere on this forum, you do NOT need to use the Repetier firmware in order to use the latest Repetier Host program. As long as you specify "“Marlin” style G-code in the slicer options, then there is no reason to change from the “Marlin” firmware that was supplied with the K8200 controller.