May I suggest that with a Sig Star series, the ST .61 will be an investment. TTs are fine engines, however a ST will take more abuse than any engine I know of. I have used STs in one way or another since back 1961.
Every so often I try other engines and find a number that do well in their intended purpose, yet for general sport and scale flying, a Tigre does the job well. I have some that are 30 years old and keep on running. I have gone to the "Chest" opened a drawer, pulled out an engine just laying in there that has not been run for 15 years or more, drop it in a plane, go to the field, start it on first flip, check the NV setting and start flying. For reliability and dependable service, I have found nothing to compare other than a well-broken-in Fox.
Tower has some good prices on Tigers right now. The .61 ringed is a bit more finicky for the first couple hours than I remember the ABC being. Been a long time since I started a new .61 ABC. Now some say the .90 but that is too much for a 4-60. OTOH the .75 is my very favorite for the .60 size models.
You might wish to consider planking the LE of the 4-Star. Makes for a much better wing. Cap stripping the ribs also adds to the rigidity of the wing. Another little item to enhance the 4-Star is to cut 2-3" off the aileron tip and glue it to the wing TE with about 2-4* up. Looks weird but definitely enhances the landings when using medium to higher pitch props.

One ST point: With the slide muffler, DO NOT push that muffler all the way in. Either cut the manifold, drill a couple holes in it/or slant it, or keep the muffler at least 1/2" out on the manifold. Failure to do so has made for some good deals for me on eBay. I have a significant number of STs from .15 to 2500.