Personally I think it’s rather meaningless to compare rates for different durations. Instead, you can try to compare them with “free market” interbank rates to determine the markup in each case.
Here I have started to sum up the sources for the latter:
P.S. another reference I use is the best interest rate of savings account (duration equivalent of SARON) and of medium term notes (usually Cembra), which are duration equivalents of fixed term mortgages. These are the best rates that you can earn as an individual investor.
P.P.S. My first impression from these data after I made a quick comparison once, is that for durations longer than 5-6 years, the markup really goes up.