Quote Originally Posted by KyleG View Post
Slight aside but I'm happy to be directed to a different resource.
How much does everyone being 20 in main stat by 8 affect the difficulty the dm should be throwing at the table vs say the 18 or even everyone on 16 (players likely taking feats?
I mean let's go basic with fighter, rogue, wizard and cleric L4 and no ones on 18 primary start...does that affect the difficulty the dm should be throwing out there vs the party with 18 or (let's go crazy) 20 in primary stat?
It depends on what you think of as encounter design functioning normally.
If you take that medium encounters should be the norm, and to never use a higher CR monster than the level of the party, then challenge will need to be upped.

If your of the mind that easy and medium encounters are, at best, meant to cause HP damage that may or may not require healing resources. And deadly is meant to be used to provide significant challenge to the party.
20 by 8 is perfectly fine, and should be mildly expected (feats being used, likely will push this down).

Both are given as system expectations in the DMG for encounter design, so dealers choice.

I have personally found the system structures are generally fine with hitting 20 by level 4, and 20 doesn't cause system distress at any level of play (probably why its the cap).

Note if you use the dmg encounter rules as written, you could probably have a party with a stat ceiling of 8 and be fine, it is very conservative in terms of challenge.