Research Assistant Professor vs Post-doc
I think you need to think about what that post-doc position can really offer you. Going from a 25th-30th University to a 9th-12th University isn't that significant, since the precision of ranking schools is iffy, at best. Therefore, think about what opportunities the post-doc will offer you: exciting research? Connections/contacts? Does the PI have a solid track record of post-docs getting tenure-track positions? On the other hand, being a non-tenure track research professor may be the better option if you think you can get enough data to apply for a grant. The bump in income is nice, too, especially given the high cost of education in the USA. I'm guessing you probably don't have student loans from grad school, but what about undergrad?

tl;dr- Post-doc:may lead to tenure-track job, possibly better contacts? Research asst prof: may lead to tenure-track job, but with better interim salary.