Deal spotlight - seeking advise from experienced investors

[Conrado Petrov]

Hi; I found a great duplex in a class A location. neighborhood is great, great schools, parks, etc and appreciating. Property listed at $675,000; both units rented revenue $3850/month. Expenses are insurance $3800 annual, taxes estimated around $8,800, landscaping/water $240/month, 5% vacancy costs; 

According to my math, cash flow would be negative -$210/month with 20% down @ 4% interest rate. Cap Rate 4.21%

Now if I offer $550,000 for the property I could cash flow $267/month with the same 20% down @ 4% interest rate; Cap rate 5.17%

Is offering $550,000 too crazy of an offer??