The question as posed is a layup. You don't need group think to answer this one. If the only thing that really matters is track performance, the Civic Si shouldn't even be in your consideration set. The better question is: (insert a comparator - Golf R, GRC, EN, ITS) or Type R? Help Me Decide.
Not sure how prices are now, but 3 years ago dealers wanted a $7k premium on both the Si's and Type R's. The Si's weren't worthy of the extra premium, so I went with the R and never regretted my decision.
I looked at both cars back to back and the fit and finish on the R was way better.
Also the R's K20 looks way more stout than the Si's L15, which is derived from a Honda Fit engine. "I Do Cars" has torn down both engines on his YouTube channel, so you can judge for yourself.
Sorry, but I'm going to go on a rant so maybe just ignore this post...
The Si and TypeR are two VERY DIFFERENT cars. When people ask this question it sounds like ignorant flexing $ "Should I buy a base Toyota Corolla or a Porsche 911?!?" Drama!
The Si is a fun daily street car but not trackable unless upgraded (brakes specifically). The TypeR is a great track car but to drive it as a commuter daily will probably be painful. Not only will it be $20k more, you have to factor in changing tires and brake pads often especially tracking and the depreciation of abusing the car. This is not a question about money, it's what type of lifestyle are you in. If you have a second car for commuting and money is not an issue, then a TypeR is a no brainer. If this is your only car and you're on a budget like 90% of the world, then save for your future a house or family and get the Si.