"Which electrolytes are better?"

don't have a clue, but I'll address Marlin's post anyway.

I'd guess that your blood is getting thicker as you get dehydrated, which impairs circulation and the ability to carry O2, and that is likely what causes that bit of dizzyness.  I've had that happen climing mountains a time or two when pushing too hard - I think its just not enough Oxygen getting to the brain ????

I have been touting the use of energy drinks probably a dozen or more times on here.  I think it makes a huge difference in sustained performance, especially if you are pushing your limits.  I use "Cytomax" energy drink rather than plain water - at least I will start out with it and use a quart of that before going to plain water.  Its just easier for your body to absorb the energy, and it cuts down on the "need" to eat solid foods - it takes energy to make that solid food into fuel, and your body will tend to shut down other functions a bit to digest the food - or it sits as a lump in your stomach (at least in mine). 

This past Saturday, I went to a local lake and did 3 laps around the shoreline.  I stay within a boat's length of the shore at a minimum, mostly stay within 6', and sometimes its within 3" and heeling the boat around a 270 deg turn to circle a rocky point - lots of steering, minimal "go straight"
so I only average about 3.5 mph - did 33.6 miles.  I started out with 3 pints of premixed cytomax, which took me thru most of two laps, and I started with water after that - drank a total of 2 1/2 quarts of liquid over a solid 9 hours in the sun.  Wasn't feeling any effects of dehydration though I didn't pee much.  Not super hot though, as I started out at dawn (maybe 65 deg?)  and finsihed at 3 before it got really too hot - likely was only in mid-eighties at 3pm.  Up untill I stopped at about 31 miles to eat a plum, all the solid food I ate was 4 little Hershey's mini's candy bars (little one bite sized chocolate bars).  I didn't "need" to stop to eat the plum, but the weather was holding nicely and I could afford to stop, so I did just to get off the boat seat for a bit.

Weekend before that, I went backpacking.  Hit the trailhead Friday evening at 6:45 and hiked up 3 miles to 11,000 feet to beat the heat -about an hour and a half to the top.  Did 22 or 23 miles on Saturday fueld by 2 1/2 pints of cytomax followed by another quart or two of water - that day got hot, even at 10,000 feet I was sweating a lot.  I did eat a bit more that day.  Finished up on Sunday with 3 1/2 mi to the truck.  Some blisters, but no cramping or dehydration.

  While hiking, I just hand carried a pint bottle and took a swig every few minutes or so.  While paddling, I kept a bottle handy and would drink every 15 minutes or so, when I got behind a point and out of the wind.

I never "hit the wall" on either trip, and didn't get cramps or get too dehydrated.   I think this stuff really works as advertised.  It certainly works for me, far outperforming just plain water.

I use it on all my Quetico trips, and it works about as well for my brother, though we don't push as hard when he is along.  It cuts down on the need for "big" lunches as you just don't feel too hungry, and saves a fair bit of weight in that regard.  It works best maybe, if you are pushing hard, but it also works if you aren't, just less noticeably maybe.

Is Cytomax the best thing going ?  don't know, don't care, but I would recommend it to you.  REI carries it, most health foods stores will, and you can find lots of places on line that sell it.  It does cost a lot more than water, but its worth it.

try it, you'll like it!