Asher,
You should have a zero balance due if 100% of the wages were earned in the UK.
Your AGI should be $70,000. The foreign tax credit is on $40,000. On box 12 of the 1116, subtract $40,000 x $80,000 exclusion / 150,000 total salary, as you can't take the foreign tax paid on the $80,000 you excluded. You can also exclude housing costs, which should further reduce your tax.
I've heard no complaints about <$80,000 incomes; incomes over $80,000 can be tricky to enter all the data correctly so that you don't get conked with tax you don't actually owe. I can't be specific other than to say I've seen them done wrong more often than right; and the end user alas usually doesn't have the knowledge base in international taxation to alert them of that fact.