starting point: 85 skill with 1735 skill xp needed to level.
Trials:
50 xp = leather bracer (1685 remaining)
99 xp = leather bracer x2 (1636 remaining)
247 xp = leather bracer x5 (1488 remaining)
95 xp = leather armor (1640 remaining)
283 xp = leather armor x3 (1452 remaining)
340 xp = leather helmet x5 (1395 remaining)
Analysis:
leather armor: 4 leather, 3 strips (4.75 leather)
125 value, 94.33 xp, 19.85 xp per leather
leather helmet: 2 leather 1 strip (2.25 leather)
60 value, 68 xp, 30.222 xp per leather
leather bracer: 1 leather, 2 strips (1.5 leather)
25 value, 49.4 xp, 32.933 xp per leather
Conclusion: If you are skilling up with leather only, you should continue making leather bracers. Leather Helmet and Leather Armor are not as efficient sources of xp per leather.
Trials:
384 xp = iron dagger x10 (1351 remaining)
555 xp = iron dagger x10 + upgrade x10 (1180 remaining)
340 xp = iron warhammer x5 (1395 remaining) (see leather helmet)
Conclusion: Iron dagger still beats iron warhammer. Don't upgrade.
178 xp = elven helmet x2 (1557 remaining)
337 xp = elven helmet x2 + upgrade x2 (1398 remaining)
Conclusion: Elven materials are too expensive to skill up on.
426 xp = silver sapphire necklace x2 (1309 remaining)
Conclusion: don't sell gems, craft up the ones you find.
Final analysis: You are less screwed than before if you make items other than iron daggers or leather bracers, but those are still the easiest and most effective smithing items to make for leveling. In specific detail, my leveling plan is:
1. Gather leather as I wander
2. Buy out the vendor's iron supply
3. Craft iron daggers til out of iron
4. Craft leather bracers with the remaining leather.
If you don't want to make leather bracers and iron daggers... consider making bows - they have fairly high value to material ratios.