The rules are different for the 2 types of plans. If you participate at work, regardless of your level of contribution, then you are subject to the limits on individual IRA contributions mentioned above. If you are income-limited from participating in a personal IRA, the only way to boost your retirement savings is to maximize your contributions at work.
There is also the "back door" Roth IRA, which is more complicated than I want to get into here.
