Great points, June.
10-man raiding is tuned to where you should be wearing at a minimum lvl 80 dungeon blues or better, and ideally some heroic epics / badge rewards (you can get 2pc T7 from badges), and with appropriate enchants/enhancements. 25-man raiding is a lot less forgiving.
If you don't mind a 'spoiler' to what loot drops where, a great resource for looking for gear upgrades is
www.wow-loot.com.
On going to this site, you can click on your class icon at the top of the page to see drops that are applicable to your class from regular and heroic dungeons, rep rewards, and select quest-chains. You can further refine it to your basic role and it will trim the list further (for example, selecting 'druid' shows all druid-appropriate loot, selecting 'feral' eliminates all the caster items). It's worth noting that it doesn't list 'lower' armor types dropped when searching this way. So, for example, it would not list cloth or leather items that might still represent a short-term upgrade for a mail-wearer, but is still a great starting place.