Calculated my MCA to be around a 4,400. Applying for Architecture.
(CP GPA: 3.4 || SAT: 1460 || In-state)
If SLO is one of your top choices, then definitely apply. If you do not apply, you will never know if you could have gotten in.
Is a 4,400 a decently competitive score for the major?
Your SAT looks competitive, but your GPA looks on the low side. SLO rejected over 10,000 4.0 GPA applicants last year so it is a very competitive campus overall.
You can do a search on this thread to see if there are any MCA scores listed for Architecture majors to see how you compare:
http://talk.qa.collegeconfidential.com/cal-poly-san-luis-obispo/2060363-2018-final-status.html