I was recently part way through a "frame-up" novice track bike build (low cost Dawes steel frame/fork), when I decided to go with a track/cyclocross/cycle speedway convertible hybrid (that would mostly see light trail use). I plan on leaving it mainly as a cyclocross machine that can be converted to cycle speedway by removing the brakes and changing the bars and stem (tires will remain the same for both: i.e. Kenda Kommandos). Track use, if I ever try it, will (of course) at least require a change to fixed gear and track tires if not wheels as well (I went with the strongest wheel set I could afford during the build). I also went with a 120mm long stem for track use, and am going to try a very short (50-60mm) stem for cycle speedway (very quick steering is the "norm" for this). Not sure what I'll run stem wise for cyclocross tho (probably something in-between). This hybrid will be nothing serious of course, but something that can be used for a number of different casual "racing" categories. I asked around about this "3-way hybrid" and was told that people have been doing similar road/cyclocross conversions and hybrid builds for quite some time. I was also reminded that the origins of cyclocross go back to the eary 1900s when road bikes were about all you had to work with. Who knew... As for the frame size, I went with a unit that would sorta "fit" both me and my wife (there's an inch or two difference between us). I hope this will somewhat cover both of us, and all three riding styles. However, I'm told that the higher placement of track bike bottom bracket shells might actually require a slightly larger frame size... Definitely something to think about next time... So far the bike works out nice enough for cruising the local dirt and paved trials. I haven't tried cyclocross or any cycle speedway sprints down at the local dirt oval yet. Anyway, sorry for the long post, and good luck with your build...