No,not really. You're kinda splitting hairs anyway - yes, both NiMH and Lipo drop voltage, but at different rates. NiCd and alkalines drop voltage quicker and don't really stop declining. NiMH and Lipo drops voltage the slowest of these chemistries and do show plateaus where voltage drop is real small as they deliver current. Lipo drops less and hold voltage better than NiMH. This is part of the reason NiMH bumped NiCds and Lipo is now bumping NiMHs.

If you want a 16.8v lipo sytem for your stock Emaxx, your only lipo choice is a 2S lipo of some size. It will run like crap on a single 3S (assuming you can figure out how to wire it) cause it will be seriously undervolted. The thing you originally started out asking about does not exist in a form that you could stick in a moving rc vehicle, nothing will handle the current even a stock set of titans will pull and be light enough for an RC to move it.

There is no such thing as a 8.4v lipo being diff than a 7.4v lipo. They are the same battery, just 2 diff way of looking at way batt is rated. Go over to TRX forums and see what those guys are running for lipos. If you're going to run stock esc, it will be a pr of 2S lipos. Your decision is how big should you buy - 5000, 6000, 8000 etc. Check out rclipo.com - you will not find a lipo listed as 8.4v, they're listed as 7.4 - the "nominal" batt voltage. I don't know why they do it this way, but that's the convention, has been since before lipo came into rc useage. Lipos are sold and advertised based on nominal voltage of 3.7v/cell.

You're confusing two voltages that are really the same battery, there's not 2 diff batteries, a 7.4 and a 8.4v. RCLIPO is one of the top lipo internet sellers, but check any of the other lipo sellers/manufacturers CBP, SMC, Orion, Maxamps, Flightpower, Trackpower, Elite, Hyperion etc, you won't see an 8.4v lipo listed.