The internship was in Seattle, but I've lived in Northern VA before college. Still, I've never been financially independent around here. Waiting a little sounds best.
I think that's a good choice given that you've never worked with the people in that particular office and that you have no idea about living costs in DC.
To elaborate a little, I do not want to "kill" your dream, and I know that coming fresh out of school low 90's with signing bonuses sounds awesome. However, you'll be living in one of the most expensive areas in the country. Furthermore, being a single renter you'll be f'ed to the wazoo on your taxes. Low 90's put you squarely in the 25% federal tax brackets, in fact you're almost touching 28%, the standard deduction and personal exemption will put you just below 28% tax bracket, but I'm thinking that signing bonus/end year bonuses will bring you back into 28% tax bracket. Plus you have to consider state tax bracket as well - looks like DC starts taxing you at 4% and goes to 8.5% after $40K, so you'll be paying 8.5% on $50K of your income. And then you have to remember about Social Security, Medicare taxes and high sales tax as well. Trust me when I say it, after DC rents and all the taxes, that 90's figure is going to shrink by a third just because of the taxes, my rough calculations say you'll be paying about $6,500 to the state, about $19,000 to the feds, and about $6500 to the Social Security and Medicare. The actual amounts may vary a bit depending on your bonus/deductions, but you can realistically expect to pay about $30K in various taxes. I don't know about rents in your specific area, but it looks like you should expect to pay about 1200 for a 1 bedroom apartment, add another $1K for bills, food, eating out, misc spending and it leaves you with about $30K of "disposable" income assuming you're putting away $0 for retirement. Once again, that sounds like a fair amount left over, but that number is before any retirement savings, any vacations, and any "toy" purchases, be it new computer/monitors/tvs/home theaters/skis/snowboards/mountain bikes.
I do not want to sound like an old man, but given your high income tax burden, I would advise you to actually max out your 401K/403b, and when I say max out I mean put away $17,500/$18,000 for 2015. After you cross $50K income threshold you're paying 41.25% of your income to various tax bodies (25% feds, 8.5% state, 6.2% Social Secutiry, 1.45% Medicare). It makes sense to reduce your taxable burden now as much as you can and it pays to start saving early. With the 40% tax burden those 18K would only be like 10K actual income if you actually decided to skip retirement contributions.
In short, I believe you made the right choice to wait a year or two before splurging on a fancy car like that. Wait to see how you like your new job, your new coworkers, wait to see how much disposable income you will actually have left after all the taxes, bills, and living expenses. As I said before, if I were you I would put away the max, i.e. $18K in your 401K, at your income level and at your tax bracket you won't miss it too much. If after a few years you feel like you can comfortably make the 435i M-Sport car payment - then go for it.
PS congratulations on coming such a long way and landing a good paying job straight our of college.