I recall advancement slowing to a crawl after 7th or so. As a DM, I realized that monster XP was basically irrelevant and I had to give out huge amounts of GP value of treasure for the PCs to advance. And even a dragon's hoard averaged around 50K GP, which was then split among 7 PC's. Most monsters, even in the Expert set, had much less than that. Monsters that tend to have little treasure (wandering monsters, unintelligent monsters) do nothing for advancement.
Then again, giving out lots of gold is not a problem as the Expert rules explicitly state there are no magic shops (Companion blurs this a bit but I think those values were for individual sales, not wide-selection shops). The most the PCs can do is build a castle, buy a ship, hire an army, or something like that.
Weapon Mastery was a great addition with lots of neat features. My brother's elf PC loved the Impale trick with the trident. Are you using weapon mastery? That would give the PCs an edge, but training rules left a lot hanging on that one die roll.