Is your primary goal a higher immediate salary?
One should give careful consideration to the likely pecuniary outcome of an MBA program. Even on a gross basis, an MBA program faces an uphill battle against a base salary of about 115K. Consider, for example, the MBA recruitment stats for an extremely strong program like Wharton, where the only functions with a median salary above 115K in 2009 were Private Equity and Consulting/Strategy (of course, one could argue that the her salary would be above the median, but the median is a useful starting point). One would also need to consider the different bonus structures for the two positions, but it is difficult ex ante to say what these differences would be. Once one adjusts for the tuition and income foregone of an 18 month program, the MBA branch would need to overcome a deficit of some 250k plus. On the other hand, the MBA branch would also presumably feature faster salary increases (but also the disadvantage of two fewer years of experience).
Another advantage of waiting is that the experience of managing other employees would likely improve one's subsequent application and employment prospects.