I think I'm going to take a chance on the maltodextrin / electrolyte mix, but will forego the whey protein. The whey protein might be something I want to add later. We'll see. Right now I don't see it as a critical ingredient, as I get plenty of protein off the bike. I'm not saying it doesn't provide added benefit. I'd just prefer to first see how the maltodextrin / electrolye mix compares to Gatorade powder (in terms of on-the-bike performance) without the added variable of protein powder.
I plan to try the following mix in my bottle: 700ml water, 100g maltodextrin, 1/4 tsp. pink himalayan salt, 1/2 tsp. magnesium citrate, 1/4 tsp. potassium chloride. That mix (per 750ml bottle) will provide ~380 calories, ~94g of carbs, 590mg sodium, 210mg magnesium, 600mg potassium.
I'm also going to purchase some Hi Lyte electrolyte replacement tablets as a secondary strategy to make sure I get enough electrolytes. They do not dissolve in water, so they must be swallowed as a pill. However, for longer rides and on extremely hot days I'll use these to supplement the electrolytes in the bottle.
This is obviously still a work in progress, but I think the new plan is progress and I look forward to comparing the results. I'm going with this formula starting in January and will evaluate my ride data at the end of the month to see if I make any tangible performance improvements. The "success" of this experiment is just as much about how I feel on the bike as it is about actual performance, but I expect that if I feel better on the bike that should translate to some degree of performance improvement.