F50 vs financial start up offer please help!

I currently work at a f50 company in risk management with great pto and benefits and decent pay. It is a specialized industry which gave me this opportunity. I recently got a job offer from a small start-up financier in the sector I work in. It is backed by quite a substantial amount of money and currently has 15 employees. This comes with a 50% pay raise and great benefits (slightly lower than current). Would you take it? I like the pay increase and I am currently 2 years out of advancement due to internal factors so it will be quite some time before I advance here. Would you give up the name brand to jump into a start up finance company with a great culture but long hours and significantly more pay? I am intrigued because starting out on the bottom if it grows to what they want it to I would fast track my career, however, there is always some risk in start ups regardless of backing. Just looking for some serious advice on this, as this could be a life changing experience.

Thanks!