No.
Depending on your Hardware (Chipset, Motherboard, Video Card, etc) there will be some variation in the max.
3.2Gb to 3.5Gb is common with some slightly more or less.
There is very little you can do to change what is seen.
In general NVIDIA Chipsets can access less than Intel Chipsets.
My guess that is gue to the SLI support, but I'm not sure.