The Royal .25 would be the pick for a JKA kit. A .25 will really haul it around and a .15 will not quite cut the mustard. For an SSC engine the TT will work but is slightly less powerfull than the OS la .15 for SSC. Mine turns about 16800 on the Standard MA 8x3 prop if you bumop the nitro upto 30% you can get a nice 17400 out of it which is perfect. Your OS la .15 should turn the 8x3 to about that with 15%. The JKA kits do not have enough wing area to qualify for SSC. A scratchbuilt warbird or MiniChoker or Bandito would be good choices. Also the new Pirana kit from Down home RC is a great SSC plane.

Good Luck