Did you end up buying the 4506? Or are you still considering it? I remain a fan of the S&W 3rd generation: reliable, strong, and accurate pistols, all of them.
If you're looking for a carry gun, the 4506 is big, heavy and hard to conceal. You might go with something like the new Glock 30S (in .45 ACP, not an easy shooter, but the slim frame makes carrying easier) or perhaps the Glock 23 (in .40 S&W and with a slightly larger frame, it's a much easier shooter).
If you're looking for defense, the 4506 is easy to shoot and very reliable, a great choice.
One key point: whatever gun you carry, you need to be familiar with it. Really familiar. It takes 2,000 to 3,000 repetitions to build a muscle memory of a skill. So, you carry a 4506, you need to practice the draw (moving from holster, to ready pistol, to safety off, sights on target, finger on trigger and squeeze) a couple thousand times so that if you ever really need it (when you're under pressure, and the adrenaline reduces your fine motor skills and brain function) you will be successful in using it.
A gun without a safety (e.g. Glock) is easier/simpler to employ from the holster. The "safety off" step is often forgotten in the heat of the moment....you should see the folks who carry an M-9 for a living forget that one at the range...it happens... If you practice enough, then no worries either way.
A few rounds at the range qualifies you to punch holes in paper under zero stress. If you're going to carry, you need the couple thousand practice draws and at least a thousand rounds at the range under timed/stress fire...