You have a point, and not a bad notion at all! But Sierra GameKings are not built like a Partition, and I agree it's a better choice for deer if you're committed to using a 200-grain pill. I'll never say you're wrong if that load works the way you want it to!
I won't lie, I've had a couple of friends experience poor performance on bigger critters with the GameKings - accuracy is not an issue and seems like they do well on deer - but I'm told they just did not hold up on tougher critters. So I've never really spent a lot of time with 30-caliber sierras except in military-style competition with a 308. I think if the 30-06 deer hunter who started this thread got the 200 SGK vice the 200 partitions he probably would come out ahead...but then again if we start talking about other bullet choices for deer with a 30-06 we could fill volumes!
The Partitions were originally designed for tougher critters, and (if I may) - when you start talking about any bullet with SD over.300, my statement about not expanding on lighter animals might hold water at shorter distances, too. Certainly not knocking the SGK! But If I was specifically loading a 30-06 with that bullet for deer I think I'd look for a 150, 165 or a 180, more or less the weight classes that 30-06 seems to excel with. To be honest I use a 30-06 and a 180 here in Michigan and have never run into problems on crop damage control hunts where we routinely try different combinations on deer out to 500 yards. I believe the 200 does have less wind drift, but any good 180 with a good BC will hold its own.
Just curious - what powder/primer/brass are you using to get 2685 with that 200 SGK? Definitely a high-end load for a 30-06 with a 22" tube! How's the accuracy?