Can anyone tell me if there are any feather or strength spells anywhere?

I'm sick of the feeble amount of encumbrance that Bethesda has 'blessed' us with.

And yes, I already have found & activated the steed stone but it's still not good enough!

I don't think so. Other than the steed stone you can also have carry wait enchantments.

Yep; there's a fortify carry weight enchantment.

No feather but you can enchant boots with a little and potions exist too.

See: http://www.uesp.net/wiki/Skyrim:Fortify_Carry_Weight

Also - if you're over-encumbered and need to hoof it back quickly to a merchant, turning beast mode (Werewolf) is a really good option. You can cover insane ground very quickly.

Ok guys, this has all been very helpful.

Many thanks

Just with stamina, steed stone and the pickpocket skill I'm at 600 carry weight.
If I add some to my gear via enchantment it'd almost be too much.

The lower carry weight hasn't affected me that much? I'm a loot-hound, but now that Bandits don't all strut around with Daedric warhammers, I can usually loot a couple of dungeons before needing to head to town and unpack.