mcbeth,
We have a similar background, and in similar situation I left my job to go for it. I'll share my story here:
After graduating from university, I joined HSBC's international management program where I worked for 3 and a half years. I was living the dream: getting paid a six figure package, living in a nice house and working decent hours (i.e. I had most evenings and weekends free and about 6 weeks of holiday a year). In a large organization like HSBC, getting work done takes time and a lot of consensus building. Sometimes the pace got frustrating but this was compensated by getting to travel the world. As part of the international management program, I moved to a different country about every 2 years to work in a different part of the bank. Traveling when you're young is exciting. I didn't have a girlfriend and in the short time I was with the bank, I lived first in London for 2 months, before moving to Shanghai for a year and a half and finally to Mexico City for two years.
3 months ago, at 25 years old, I left my job to start learning to code from scratch and start a start up. I left for some of the reasons you gave: politics was getting worse and I found myself taking more time trying to convince different parties and teams of my work than the time I took to do the work itself. But I didn't leave because the bank was so much more political than it was when I had started, I left because I wasn't prepared to put up with the politics and the red tape anymore.
The difference was that I realized I didn't want to work for anyone anymore. 2 years ago, while living in Shanghai, I stumbled into the local start up community and befriended some start up founders who completely changed my perspective on life. Until that point, most of my friends had been working in banks, consultancies and law firms. It was normal to sometimes spend 6 months building consensus and convincing teams to work on a project that might only take 1 month of effort. We accepted that it was normal for the perception of hard work to be more important than hard work or even effective work itself. We put up with corporate life because it was normal and because we didn't know any other.
The start up life I saw wasn't glamorous but it so much more exciting. While I lived in a 2 bedroom penthouse apartment in a fancy part of Shanghai, my friend shared an apartment with his co-founder and 4 other hackers he hired to work out of his living room. But unlike me, he wasn't worrying about deadlines and making a good impression. Instead, he was working on things that mattered like figuring out how to get through the month with enough cash to pay his employees. His life was the life of an entrepreneur, a roller coaster ride of emotions with very high highs and very low lows, and I wanted his life.
And so with a promising career ahead of me, I quit. I figured that in the worst case, I would fail multiple times, burn through my savings and get a job at 28. Of course, I had already decided that I wanted more than anything to start a start up.
My advice, as some have already suggested, is to find out what you value. If you value being at the top end of the corporate ladder, keep pushing, it's a long road ahead. If you value having disposable income and the opportunity to travel, keep your job. If you value your personal life, keep your job but take your pedal off the gas a little and prioritize your personal life.
If you're serious about a start up, ask yourself if you can afford to quit and then ask yourself if there's any other alternative. Start ups are difficult and demoralizing, even if you're wildly optimistic and the kind of person who normally achieves what you set your mind to.
If you're still serious, put together a budget, and see how long you can last just on your savings. If you don't have any liabilities like a mortgage or a family and you've saved some of your cushy salary over the years, you'll probably find that you can survive for a while.
For me, it came down to asking and answering these questions:
Q: What will I regret when I'm 80 years old? What am I going to regret more: taking a shot at a dream and failing, or never having taken a shot at all? (http://www.youtube.com/watch?v=jwG_qR6XmDQ)
A: Taking a shot and failing.
Q: What's the realistic best case scenario end game? I.e. If I look at someone who's 15 years ahead of my in the same career path and has done a good job of getting promoted, recognized and rewarded, am I happy doing what he's doing in 15 years?
A: No.
Q: What's the worse thing that can happen?
A: I'll get a job at 28. I'll probably make less money, but I'll at least have 3 years of international work experience at a major bank.
Q: What if you never get such a sweet job? Six figures is a lot of money for a 25 year old!
A: I don't have kids, I don't have a mortgage, I don't have debts and I do have a enough savings to tide me over for a few years. It means that I won't live with the same degree of financial freedom (e.g. watching my spending, going on fewer holidays, eating out less, etc.) but it's a price I'm prepared to pay.
For most people, the last few questions about financial security are the most difficult. At 29 without a family, you're young enough that you can start over if things don't work out. If you have enough savings and you're serious, go for it.
Good luck.