Thanks for your advice.

The car sale tax in Seattle is unfortunately high over 9%, I need to pay additaional tax on top of CA tax to match local tax if buying car there. The tax shouldn't be problem.

The air ticket is about $150 from Seattle to SFO. Driving back X5 from CA sounds great idea. I can schedule vacation time and drive this brand new car.

Whether it's worth or not, it all depends on the price premium difference between CA and WA.