>>1252800If you can't find charts and sample images comparing both lenses, then your only real option (short of immense luck in finding someone on the internet with both lenses and enough interest in helping you to go and do some test shots with both) is to simply rent the lens you want to evaluate.
You only need it for 1-2 days, anyway. You're not seeing what it's like to live with the lens. Just set aside a weekend (or just a Saturday) and schedule the lens to come in on that day. Then head out for some daytime/sunset shooting, and send it out the next day.