I have both the Certified Internal Auditor and the Certified Public Accountant designation. I found the CPA exam much more difficult than the CIA exam. Just have a look through the study material for each of these exams and it will be apparent enough to you. The subject matter convered on the CPA exam, particularly as it relates to financial reporting and governmental accounting, is very difficult. The simulation questions on the CPA exam can be very complex, particularly as they relate to Taxation.
I also have the CFE designation. That exam is ridiculously easy, on a high school level, really. The ACFE should make it more rigorous to maintain the significance of the designation. I figure that the ACFE is still trying to grow their membership and must make the exam easy for now, but that should change with time. If you are looking for a rudimentary test that will require no more than 50 hours of your time in test preparation, go for the CFE.
Also, let's be real here. Being a CIA (what's that?) is okay, but it is no where close to being a CPA in terms of meaning, prestige, and pay. What is the first question that comes out of someone's mouth when you tell them you are an accountant or an auditor? "Are you a CPA?" NOT "are you a CIA?" Sorry, fellow CIA's, but few people care that we are CIA's, even in the world of internal audit. Hiring managers care greatly if you are a CPA. I had my CIA designation before my CPA license, and I found myself constantly explaining to people what "CIA" stands for. Don't get me wrong. It is a fine designation. For now, though, it is relatively unknown, and is inferior to being a CPA. In the world of accounting and finance professionals, you are relegated to second class status for not being a CPA, sort of a "Oh, you couldn't hack the CPA route, huh?" Like that.
I was a "C" accounting student some 30 years ago, and I was able recently to pass the CPA exam on first attempt by studying 250 hours per exam section. I used Gleim. It's cheap and easy to use. That's right, a total of 1,000 study hours, repetitively answering software questions over and over until getting a 90% or better on a 50-question practice test for each section. If you do that, you will pass each section of the CPA exam on first attempt. If you are not scoring at least 90% on the practice tests, don't bother taking the exam, as you probably won't pass.
Do yourself a HUGE favor. I've hired hundreds of audit professionals over the past 25 years. Skip the CIA and save your time, energy and money for the CPA exam. The CPA designation is instantly identified as "the best." It is a highly passable exam if you put the study time into it.