Dang, yeah it gets 100-105F+ with high 90%+ humidity here for a few days here and there. You could delay that intercooler purchase for a while since you are in Alaska.
Since summer is rolling around, I still would recommend an intercooler to anyone though, it can only benefit you. These turbos are so responsive that I just don't believe in that the volume added by the intercooler adds any measurable lag. Otherwise, people replacing their change pipes would loose response from going to the tiny diameter stock pipes all the way up the the huge 2.5" pipes. Everything I've seen has shown that intercoolers in our application can do nothing but benefit you. We aren't talking about huge intercoolers that block up the front the car in this platform. Almost all these direct replacement intercoolers are still considered "small" in the world of automotive modification.
The logic with the larger intercooler adding lag only really applied to very high horsepower applications where the 700 HP turbo "Mustang" (or whatever) wants an intercooler that will cool "1200 HP" when the "900 HP" intercooler will work just fine. In this "Mustang" case, these kind of intercoolers are huge and are many times larger our largest aftermarket options. They should use the smallest size that fits the "Mustang" application without noticeable heatsoak. For our platforms, the volumes of even large aftermarket intercooler are so small that this kind of logic doesn't really apply. Different rules for different power levels.
Back on topic, the stock unit is woefully inadequate for any tune in my opinion, you lose a power on the top end due to heatsoak in any kind of track or spirited backroads driving. While you can't "feel" it as easily, since these are torque monsters down low, you lose a lot of HP on the top end past 5k RPM from heat soak. I've seen a loss of a few HP up top even in 60F weather, about a 3-8 hp loss towards redline in the second pull, compared to the first at those cooler temps. I swapped the intercooler as my first mod, before I even started heavily tuning the car. The engine just felt tired on the top end after going from a dead stop up to highway speeds on interstate entrance ramps in anything over 70 F. A FMIC is the second best mod (besides tuning) from the data I have seen.
Well, unless you just do 1/4 mile drag runs and squirt methanol in. No benefit in a larger intercooler in that case on the stock turbo. Could be a few dyno pulls out there that prove me otherwise, but I haven't seen them yet so I'll stay opinionated.
First and best mod is spark plugs, spark plugs, spark plugs. Gotta replace them stock spark plugs, their gaps are usually pretty large and the heat range is a bit too warm when you start tuning the car.
