Its a bit of a ****ty reply though isn't it?
Surely the point of a forum is to be able to ask advice from those better in the know to either peform a task you're unsure of, or glean info on products that others have experience of before spunking your hard earned on it.
If every case was "by the time you do do the job you should have researched enough about (insert topic here) it to already know, you wouldn't have needed to start this thread" then it would be a pretty empty forum.
Regarding bigger brakes giving a better one off braking performance i can't say i agree.
First off let me start by saying that if you are using the reasoning behind getting a BBK because of track use, then yes, its probably an idea for the best, as the stock setup overheats way too quickly when used in this manner, especially on smaller tighter circuits. However, if its purely because you think that on the road, everytime you use the brakes, a BBK means you'll stop a lot quicker, then thats poor judgement
If the stock setup can be utilised hard enough to either lock the brakes or get the ABS light flashing, then really thats about as hard as you can stop. Reasoning behind BBK's are because the stock setup and fluid won't stand up to repeated regular heavy use such as on track, and you'll simply overheat components causing fade and loss of braking performance. A BBK is far more efficient primarily due to its size and design of disc and caliper, and dissipates heat a lot better than a cast iron single caliper piston and 1 piece disc affair. Although the floating disc design of the Euro M5 makes some headway into that argument over its USA counterpart
Once the stock setup is up to operating temp it can easily be used hard enough to light the ABS. Given that this is pretty much all a BBK could do also, i fail to see how it could "rip your face off" when stomping on the middle pedal. This is given that pads are the same across both sets
The stock setup won't repeatedly make you feel this way i agree, due to reasons above, but those looking into a BBK under the impression the car will stop from a given speed any quicker on a one time stop test will be sorely dissapointed.
CPR based over here in the UK who work closely with Evolve cite the Ksport kits as very good value for money. Sure, they won't be up to AP standard, but they are not AP money either. IIRC they are pretty much copies of AP gear though. They are dust sealed for road use and so should last through the winter, although the standard pads that come with the kit i'm told aren't the best, you can upgrade to something like Performance Friction pads readily.
As said above, the first relatively cheap upgrade would be to use a good pad combo with decent Euro spec discs. EBC yellows over here certainly in the UK, not sure if they are available in the US, are highly recommended by a lot of track day enthusiasts over here and are certainly a lot cheaper than other pads such as the dedicated Pagid's etc. Also, they offer a pretty good bite from cold, and so if your car isn't solely a track toy (and i'm guessing as an M5 it probably isn't) it means that you won't be driving it up the nearest tree every morning when you first use the car on the road