If one's goal is coming back to SG, it seems no point to specialize in US vs SG though even as UK med grad, except it may be slightly faster.

Rads are 2+5 in UK, if you do a research year + 5y residency it is 6, 1 year shorter with a lot more work.

IM is 3+3 vs 2+3+3/4 depending on specialty, again if you add 1 more year of research then you are only 1-2 years faster with loads of uncertainty not being able to enter the specialty you want. Plus having a branded CV with training at "St Thomas' Hospital in London" will be more appealing to lay people than some US board certified cardiologist trained at Jackson Health System. To add on to that the US specialist is called diplomate vs FRCP which add further insults as you sound like someone who just took a part-time dipderm in cardiology equivalent.

So I guess the difference is more significant in things like FM which you just take 3 years to finish it off, no need research, save 2 years and easy to get in + nobody cares where you got your FP/FM/GP from anyway.