OK, so there seems to be a misunderstanding about photos and iCloud.
Your iCloud storage is used to house backups of your device, which includes a backup of your Camera Roll.
Photo Stream is a cloud-based stream, but is not intended as a storage or backup facility. Photo Stream is used exclusively for sharing photos between devices signed onto the same iCloud account. Photo Stream does not take up any of your iCloud storage.
You can have up to 1000 Photo Stream photos on your actual device, but the Photo Stream itself (in iCloud) only keeps 30 days of photos.
So, you cannot go to iCloud and find photos (right now - later, that will be different when iCloud Drive and Yosemite are in place along with the new Photo App). All you can do is restore or set up a new device with a backup on iCloud.
With iOS 8, all of your Camera Roll photos and the last 30 days of your Photo Stream photos went to the Photos library on your device. You can view them there. Also, the last 30 days of photos on your Camera Roll and Photo Stream went into the Recently Added folder.
If you had a lot of photos that were only in Photo Stream that were older than 30 days old, then they are gone. That is the nature of Photo Stream. If you had to restore your device, if your device was lost or stolen, the same would be true, and it would be true on iOS 7 or iOS 6 or iOS 5 as well.
When you did the update the Photo Stream had to be re-downloaded from iCloud and that is why only the last 30 days are still out there from the Photo Stream. Even if you backed up your device prior to the update, if those photos were not also on the Camera Roll, then they would be gone.
Because again, Photo Stream is not a storage or backup facility.
Any chance you imported your photos to a computer or a cloud service like Dropbox or Flikr from your Camera Roll regularly?
Post back with any questions.
Cheers,
GB