Need to make a decision on a job offer

I'm a Manager in Valuation at a Big4 accounting firm. Just received an offer for a corporate strategy role that I need to reply by next week. I really want to do corporate development but realize that it will be a tough switch since mostly investment bankers get it. 

I am interviewing for a company in the industry for the corp dev role and have a case study presentation to make early next week. The company has been a little slow with the interview process so there is no way I will get a response from them by next week before my offer acceptance deadline. 

Not sure what I should do since this is my first time encountering such a situation. Any advice will be greatly appreciated!