100% behind +1 up -1 down. On map flips it takes a couple of rounds for the auto-balance to even things out so there is really no reason to punish the unlucky, its nothing to do with the skill of the individual or the team when one team is accidentally stacked in the first round.
How many times have we all been auto-balanced off the winning side and onto the loosing side only to have the x5 blown to pieces.
There is no good reason for punishing the players. It can be really disheartening for new players to find them selves on the arse end of a winning streak. Having there x2 or x3 ripped away from them like candy from a baby (I'm assuming you've all stolen from babies and know what I'm talking about.)
Also that last 4million xp is a... TOTAL SON OF A BIOTCH! OMG 4 FREAKING MILLION!!!
If x's went up and down at the same rate you would spend much more time in the region of the great multipliers and so be happier and less prone to hunting chadz down with a knife, not that I would, but other people well I can't speak for them and their murderous intent.
EDIT: as for upkeep, if that is an issue with a more rounded and player friendly +1/-1 x system then compensate with an increase in upkeep costs. As the upkeep costs stand I they are not very well balanced, they aren't bad but some times it is totally random. I was wearing my best Armour kit (Tin canning it as best I could) and went for 8 rounds with out paying any up keep at all. Not to mention a bizare glitch gave me Rusty Heraldic Transitional Armour for no reason, didn't own it, didn't buy and it only showed up in game.