Ptsb 26 month or 5 year fixed

I was going to put money into the ptsb 26 interest frist account over 100 k but I notice there 5 year fixed which they would pay interest every month to me would this be a good option as I think rates will be going low for next few years so if I am getting 4.6 I'd be doing well anyone think I should go for it or stick with there 26 month instead.
I can see fixed rates being around 3 to 3.5 from late next year onwards for at least 2 years

Are you certain you will not need access to the money for 5 years?

It is a long period of time to be locking your money away for.