Quick question, I hope...

I have a redington 8'6" 2 pc 3wt
a griggs 6'6" 2 pc 3 wt.

BTW - I like them both

I have an SA reel I take along as an emergency spare, and a redington CD 3/4 I use as a primary reel.

My lovely wife got me a spare spool for my redington 3/4 as a V-Day gift from sportsmans warehouse (it was on closeout). The salesmen convinced her that I needed the spare so I could carry a sinking line to fish the deep pools and heavy currents of the Truckee.

Now, I am still a rookie, but I think he saw her coming, cause I figure if I get a sinking line or sink tip line it is going on my 5 wt. I am not even sure they make sinking 3wt line.

Now the CD reel has a WF3F Lefty K line on it, and the SA reel has WF4F airflo line on it. The 6'6" seems to cast a little further with the 4 wt, so that is kinda kewl.

So, I don't want to take the spare spool back, don't want to hurt the wifes feelings you know, but, if you had these two rod lengths, and a spare spool, what would you put on the spare and why?

My original thought was a semi decent DT3F for those times when finesse is required, but if you had seen me fall in the river last week...let's just say finesse is still part of the game I need to work on.

The question: What would you put on the spare spool and why?