You might want to try some Sweet G-90. Its a mixed yellow and white hybrid with a lot of sugar. The ears are 9 inches long and they have 16 rows of kernels. It will grow in soils with a wider range of ph from 5.5 - 7.5. Plants are 6-8 foot tall and it takes it 85-90 days to mature. I had this one last year.
This year I'm thinking of planting some Sun and Stars which is a super sweet hybrid but the ears are only 8.5 inches long but I hear it is a good one too.
There is another one that I have been looking for (I'm going from memory here so I might be wrong) but I think its called Oklahoma Silver Mine or something like that. Not really a true sweet corn but an old variety that produces huge ears but are sweet and good to boil. I used to keep this but several years ago the mice found my stash and I haven't been able to replace it. If you can find it, you might want to try it too. Not as sweet as these two mentioned though.