Thanks for the vote of confidence Inertia, and you are right, I didn't answer the question.
Despite all the horror stories Li-Po's are just batteries, like any other. The source of the power is slightly different, just some strips of polythene bag like stuff and a scraping of Lithium paste etc. You wouldn't think twice about putting two NiMh packs in Series or Parallel and the same goes for Li-Po's. Ideally they should be a matched pair and charged to the same amount.
In fact in multiple celled Li-Po battery packs, each cell is linked to the next in Series inside it anyway, with a common earth to all individual cells and a power lead from each cells' positive, hence the little white balance plug. Say an 11.1 volt Li-Po, then 3 positive wires and one on the end, usually black being the common negative. (The 3 positives can be any colour in fact)
Remember Series wiring, ie. daisy chaining one cells' positive to the next cells negative will increase the overall voltage but capacity (How long it lasts) will remain the same. In this sense you will use the black output wire from one pack and the red output wire from the other to connect to your speed controller. So two 11.1v x 2500 Ah batteries would supply 22.2 volts at 2500 Ah, This certainly wouldn't slow down the startup speed, which was the original question. I would suggest it is safer using a 6 cell battery (22.5v) at 2500 Ah if you want that effect.
Extending the running time without doubling the voltage ie 5000Ah at 11.1v means running them in Parallel, which I do all the time and a made up 'Y' lead which couples both cells to each other black to black and red to red is safe and works well.
Action do some very nice connection boards with fuses etc if you decide you want to start cutting plugs off, which I don't like the idea of as then there can be charging problems.
Treat them like ordinary batteries, use the proper rated cables and good quality plugs which are soldered, lipos are capable of discharging their whole current in a split second if you short them out, that means Bonfire Night comes early if you cut both plug leads off at the same time!!
Good luck.