I would like to price a European option with maturity equals to 5 years. To do this, I'm using the Black-Scholes model with stochastic interest rates.
Suppose I choose the CIR model for the risk-free rate. My question is: should I model the entire term structure of interest rates, or I can just model the 5-year rate?
As a side question, which one would be considered a good proxy for the 5-year risk-free rate in the US?