I've gone though the classroom training for PMP using PMBOK4 syllabus however since the exam now will be based on PMBOK5, is there a chance that I might be risking the exam with only my references from PMBOK4?
You will certainly not need another week long class unless you were having see issues with the basic concepts. Pick up the new version and study it and go take the test.
Even though PMI allows you to use the 35 hour contact certificate for exam registration for the updated PMP. The project management knowledge has been expanded/re-organized from PMBOK 4 to PMBOK 5. Major difference being:
- 1 more Knowledge Area (Project Stakeholder Management)
- 5 new processes introduced
- 19% increase in ITTO (total 614 in PMBOK 5)
You will need to study really hard by reading through PMBOK 5 and/or other updated reference books. You will need to especially note the different as management of stakeholders has been separated from other knowledge areas and stand on its own. Answers based on PMBOK 4 in this knowledge area will be wrong. But for other knowledge areas, the general framework is more or less the same. In the end, PMP exam tests candidate on how to apply the project management knowledge instead of memorization.
For more tips on how to prepare for the PMP based on PMBOK 5, you may read this report on PMP exam study tips.
Of course it's a risk and the risk being you might loose out on any concept which is new in PMBOK5.
More over PMI does not mention weightage of each topic or passing percentage so its very difficult to quantify the Risk.
You will be paying few hundred dollars for the test/exam, so monetary risk is those few hundred dollars.
There is a risk but it is same as it was before. You should read this article - http://www.pmbypm.com/pmp-training-again/
It is noteworthy (in addition to the existing answers) that the current PMBOK Guide (Fifth Edition) got an appendix to cover the differences to the previous edition: Appendix X1 Fifth Edition Changes. This is the best place to figure the differences out and focus on learning these.
It might also be a good idea to apply for PMI membership prior to the exam and thus get the complimentary PDF download of this standard.