Just starting out with sfml myself and learning my way around it. I should point out that the GetFrameTime() function has been removed in the new version (2.0) as they didn't think it was accurate or needed. It is recommended that you use the clock class, most common way would be to get the time since the last call within the main loop and pass this to any functions that would need to know it.
I would also personally assess the performance of the function of the time that you are spending within it rather than CPU %. You can do this again with the clock class, reset it at the beginning of your draw function and then get the time at the end to see how long you spent there. You can then decide from this if you are spending too long in this function.
I'm unable to find the source again, but I recently read an article about an indie team of 4 running on a budget of about 15k per month -- They had office space (so budget for rent, utilities, snacks, etc) and legal/business council, both accounting for around $1200 of the monthly budget each -- a small start-up team .