How to evaluate deal with multiple loans?

[Andrew Herrig]

I recently discovered that I can take out a "loan" from my 401k at my day job at the Prime rate (currently around 3.25%). This seems like a good way to get access to some cash to put 20-25% down along with a conventional loan on a property.

My question is, how do I do a financial analysis on potential deals when using essentially two loans of differing terms? The conventional mortgage would be 30 years at, say, 4.5%, and the 401k loan has a maximum term of 5 years at 3.25%. I generally look at cash on cash returns to compare deals. Is this a situation that IRR (internal rate of return) is better at handling than ROI?