What kind of experiences you have?
1-5-2 (TMPGEnc default)
1-4-2 (pal dvd)
1-7-3 (dvd-hq's max rec.)
or
1-9-4 (50 frames)
when "Detect scene change" is on?

In general longer gops should give better quality, when datarate is limited
to svcd max, but I've got better results with shorter gops. Why?