BCRider

The seat going forward moves your core further ahead and the support from your feet on the pedals doesn't support your weight in the same way. The seat has to hold you in the proper relation to the pedals as well as the bars. In fact I'd say that you need to set the saddle to suit how your body works best and balances best over the pedals. Then alter the stem to move the bars as needed to suit your reach.

I've no idea if it's right or not but I found that the bikes I feel the most comfortable on are those where I can lift my self just barely off the saddle and almost let go of the bars and I'm balanced quite finely over the bottom bracket where I tend to fall forward or back quite evenly. This being for a semi upright posture. I'm not sure what the equivalent "sweet spot" is for a rider in the drops on a road bike. But I suspect there is one. Whether or not it is when the rider's center of gravity is directly over the BB or not I can't say.

If it's your weight on your hands which is making them go numb I don't really see how a shock absorbing stem will help. It's not the shock but the weight that is causing the issue. Or perhaps the wrist angle is not the same. Perhaps when in the drops you're reaching more than you used to. Maybe not flexing as naturally at the hips as you used to. If you feel like you are reaching to the drops instead of having a pretty natural and non strained stance this might well be affecting the angle of your wrists and that is what is making your nerves go numb.