If memory serves, you should have the OEM size of 235/60/16 on your car. That being the case the best "plus 0" (going wider but staying on stock rims) is 255/55/16. Unfortunately that size sucks as far as tire selection. (unless you want to go with the truck based Pirelli Scorpion Zero which is the PZero Asm for trucks)

That being pretty much out of the question for a W140 the next closest size for stock rims would be 245/55/16. In that size you have the Michelin Pilot HX MXM which is the best ride+handling tire out there. Others can ride a little bit better, a few others can handle a small amount better, but nothing else combines them as well. Downside is they cost and wear like a performance tire. ($238 at Tirerack) Since the only other tire in that size is the notoriously crappy P6000 for $210 it doesn't seem like that bad a deal all the sudden. The only negative to that size is it is 1.8% shorter. Though not a big problem as 3% is considered the amount of variance tolerable in a benz it is still a bit shorter. (think shorter gearing...) At 100kmh your speedo will be reading 1.8 kmh fast so in reality its no big deal.

The "flip side" is 245/60/16. This option is 1.7% taller than stock. I would NOT recommend going with this option as its usually a bad idea to go wider and taller at the same time. However, its a moot point as there are no tires I know of in that oddball size.

To get a more hardcore performance tire you would need to go to 17" or 18" (or more!) sizing. If I had to pick one tire to be available for your car it would be the Pilot HX MXM so you are lucky there. As far as outside shoulder wear...next time you get your car aligned ask that toe-in be kept to min-spec and ask them to please dial in as much negative camber as stock adjustment will allow. That will help both handling and front tire outer shoulder wear.

Hope this helps...Lee