I understand that being 28/29 and wanting to get the show on the road plays a huge factor in choosing St. George's over SFSU....
But the 2 extra years is definitely worth the security of being a US med grad. Especially if you're fairly intelligent and can achieve a good GPA and MCAT score, why would you want to deny yourself the chance at getting into a great US MD school? Plus, all that BS that comes with being an IMG...that would be enough to convince me to stay in the states. By becoming an IMG, you'd be really shooting yourself in the foot. You want to open doors, keep yourself in a good position to obtain competitive residencies in desirable areas after med school. From what I read/hear, being an IMG really limits you heavily, especially nowadays with new US medical schools opening up without new residency slots. My 0.02.
"An investment in knowledge pays the best interest." - Benjamin Franklin