Right now I have the yellow springs (JPS 3.5) in my JP trigger. I really like the trigger pull. I was looking at their website and see they also have a little heaver set (JPS4.0) that they say is better for cold/tactical applications. I plan on using the lower for fox/coyote hunting this winter. As for tactical I would rather be prepared than not, if you know what I mean.

Quote taken from their site:
Note: If you are ordering for an Armalite AR-10 or Knights SR-25, Bushmaster 308, DPMS LR-308 or using your rifle for tactical or cold weather operation, specify the JPS4.0 tactical spring kit with your order. In these rifles, a heavy hammer spring is necessary for ignition reliability and to eliminate the finger bounce "doubling" possibility.

For reference also from their website:
JPS 3.5 AR reduced power spring kit
JPS 4.0 JP Tactical Spring Kit, 4-lb pull with JP fire control parts

Being in Minnesota, where it gets cold once in a while in the winter, does anyone see a huge advantage in going to the heaver springs in my trigger.

I have a pure match rifle for 3-gun use fitted with a JP trigger, including the JP yellow springs. The trigger is awesome, BUT on rare occassions I have had light strikes with old foreign surplus ammo. Solution: I don't use surplus ammo in this rifle.

I have a hybrid match/SHTF rifle fitted with a JP trigger, but with original GI springs. The pull is a tad heavier, but I feel comforted by the harder whack it gives the primers. The trigger pull is still miles better than the original GI trigger pull.

I've shot many thousand of rounds with the JP yellow springs.  As long as you run a lightened hammer, you should be GTG.  

You can buy the JP lightened hammer or just cut the "tail" off the stock hammer to lighten it.  DON'T take off any metal at the engagement points - just cut the tail off.

The hammer tail is unessesary on a semi auto rifle.  

Or you could Just install the springs back in that came with your org hammer trigger. They will be the same as the tac that JP sells.