I've been GMing for about 15 years now and one of the hardest part for me is finding a good balance of difficulty for players that are in their 3rd + career.
By this time elf's are getting close to 70 80% chance to hit on WS. In some games I've had players break the 100% mark and couldn't possibly miss unless they rolled a critical fail of 99 (house rule)
The problem I find is those that go the academic route don't get plus 20 or plus 30 to WS or BS; for the most part they stay a little on the squishy side.
Some players are running around with plate armor and reaching AC+T of 10+ while our not so strong players are running around with mail shirts and other AC boosting items; still not matching that of a fighter oriented player.
To keep things challenging I have bring in enemies that hit a lot harder and more often increasing the chance of a squishy getting one shot by a critical.
I normally combat this with giving them a puzzle during a epic battle that needs to be figured out or more and more enemies will descend onto the party; but sometimes the dice come after them and soon all hell breaks loose.
I'm just curious to see how other GM's handle this. Most of my games are combat focus but every now and then I have a group that rather RP there way through a story rather than engage everyone and there mothers.