Importance of GRE for computer science PhD applicant
Admissions committee in strong CS PhD programs are primarily looking for concrete evidence of research potential.  Neither GRE scores nor the ability to take lots of undergraduate classes provide that compelling evidence.  Fortunately for you, a first-author CVPR paper and strong recommendation letters would!
Given your research record and the likely strength of your recommendation letters, no admissions committee is going to care about your GRE scores (even if the ongoing pandemic allows you to take the GRE in the first place).  At least in the top 10-20 CS PhD programs, GRE scores only matter if they are really bad, or if your case is otherwise truly borderline.  My department hasn't required GRE scores for graduate applicants for over a decade.
Similarly, I don't think finishing early will have much effect on your chances.  A few people will be impressed, a few people will be concerned about possible burnout, but most people won't care, especially given your research record and the likely strength of your recommendation letters.  Unless you have financial reasons to finish early, you might be better off in the long run staying where you are and expanding your research portfolio.  (If you eventually apply for academic jobs, hiring committees won't care how quickly you finish your PhD; they'll care primarily about the strength of your research record.)
This is a great issue to discuss with your letter-writers.  See also Mor Harchol-Balter's detailed advice for CS PhD applicants, based on her experience at Berkeley, MIT, and CMU.  (Her description also matches my experience at Illinois, and other departments like Washington explicitly recommend her advice.)