i looked up a number of datasheets, trying to find out how long it takes for each vga card to perform a dram read/write, and come to such a conclusion, but not sure if i am reading the charts right:
2 clocks per read/write: cirrus5320 and later, et4000, oak087, s3 801, wd90c11 and later.
3 clocks: chips450 and 65545, trident8900d and 9000. note that chips have higher mclk than typical cards.
5 clocks: wd90c00, unimpressive, probably not going to be fast in svga modes.
7 clocks: chips451, oak037, no wonder why they are that slow.
cirrus51020: varies between 4 to 7 clocks, condition not understood yet.
chips441: varies between 5 to 6 clocks.
unlisted cards are due to short of datasheets.