Depends on the chipset.
440BX systems don't run well at 133FSB with all four DIMM slots filled. If anyone's actually running a 440BX at 133 with all four DIMM slots filled, please let us know what DIMMs and what board. The problem isn't the RAM, it's the chipset.
The best I can do is 124FSB with my P3B-F, all slots filled. If I push it to 133, I have to drop to filling only the first and third DIMM slots.
The i815/E only handles two DIMMs when over 100FSB, as per Intel's documents on the chipset. I've gone up to 153FSB (the max on the SE6) with two DIMMs, but I had to retard the RAM speed by 33Mhz (120Mhz). It did 140FSB no problem with timings of 2-2-2-6/8. The board could never do timings of 2-2-2-5/7 unless I was at 130FSB or below. 133FSB, no good on 2-2-2-5/7 (this is CAS2 Crucial PC133 non-ECC RAM, mind you).
The P3V4X took four 128MB ECC PC133 DIMMs to 146FSB for me with no problems. The DIMMs were at CAS3.
I did try my SE6 with a 256MB ECC and non-ECC DIMM, both rated for CAS3. They could do 133, and 137, but nothing higher. I was a bit surprised to find two 128's doing better than one 256, but it could be the board - my SE6 is in the process of being RMAed, as it has flaked out (spontaneous reboots, RAM count in POST doesn't work, etc).
Just my $0.02