So I play in a game cash game where the buy in cap is up to the biggest stack at the table, which in turn regularly results in the table STACK AVG being around 300bb. My standard open size is 3x from all positions but I'm wondering what sort of adjustments I should make when stacks get so deep.

I look at it 2 ways either we can start opening wider with more speculative hands that have nut-potential, or we can can open 3.5x~ at 200bb avg stack and 4x~ at 300bb avg stack with a fairly similar range. If the table is softer then I think the former strategy is the better option, and if the table is more solid then probably the latter option? What is the theoretical adjustment at these stacks?

"Speculative" is more subjective than you think. It's often the case that certain hands move into and out of different ranges depending on stack depth.

As an extreme example think about small/medium pairs.

At say 80ishbb and up (rough number no analytical proof) depending on opening size or action you can play them to set mine. Get into the 55-60ish bb range and they can't be set mined or shoved profitably. Get below that and you can start shoving some of the medium pairs profitably in a short stacking strategy and get much below that and you should always be shoving them, like short stacks in tournaments.

When you are deep post flop play is much much more important than deciding on opening .5-1 bb difference. I have heard in general even at 100bb varying betsize preflop by a few bb doesn't greatly affect EV as most of your bb will come from larger pots on turn and river.

At deep stack depths your #1 priority is protecting your stack. That doesn't mean you play scared it just means that you need to adjust your relative hand strength up slightly (depending on villain's tendencies, actions, etc.)

You should also explore strategic options that don't often come up in 100bb games like defending ranges for multiple raises with money behind, over betting on multiple streets, extreme overbetting, and how best to get your whole stack in with the nuts and what bluffs make sense.

Most frequent adjustment for deep stacks, imo, is that even on the river mostly you will have to play a full strategy of betting with raises and checkraises that are significant but less than all-in. SPR will be higher. Less decisions are binary, bet sizing less than all-in is the norm and the skill cap.

If players are getting all 300bb in the middle with any regularity, then you should be patient and wait for the nuts. It is all about adjustments and which players can adjust properly to 300 deep.

If you get pinned down with the second nuts, play some pot control. Salvaging a third of a stack instead of losing it all is also a skill.

Discipline.

thanks guys appreciate the answers

I was going to try to find something smart to say and then I got schooled. Great answers guys. Thank you.

I looked into this and its surprising to see that if you open 4x and pot the flop and turn then the pot on the river will be 85.5bbs whereas if you did the same but raised just 3x preflop it would only be 67.5bbs. 18bbs, a pretty sizable difference, if you consider you're playing with an edge then wouldn't opening bigger preflop when deep-stacked actually increase your EV? And given that you're deep-stacked not take away from your edge?

All 18bbs will rarely all belong to you at showdown and technically 9 of those bb were contributed by you. Also nothing says you can't oveebet any or all streets of you think you can support that strategy.

I also never claimed that you can't adjust your open sizing, just that it's unlikely as important as leaning how to play the other streets when pots are much bigger and there is still money behind.

You should definitely look at adjusting your preflop raise sizes (3-bet and higher) a bit higher depending on position.

Assuming your edge is the same regardless of stack depth and you don't prevent yourself from putting in all the money when it is appropriate to do so your preflop open is mostly inconsequential to your final EV. You can pick whatever sizing you like within say 2-4bb or even vary your sizing if you want.

If you are opening oop to deep stacked players I would assume you'd want to open for a smaller sizing--not a larger one

Aah okay thanks for explaining, and yes I 100% agree postflop is way more crucial to your bottom-line EV, I was just considering the idea that a bigger PFR can be slightly higher EV but yea I tend to agree with you on this actually, I guess in a no-limit format it doesn't matter all that much due to overbets.

thats a good point

When stacks get 100bb+ I like to open a lot more suited gappers in position. When stacks get 200bb+ you wanna get into a nut vs nut situation so you can scoop the big one.

Eg. AA vs KK

Eg. flush over flush by playing Ax suited and Trying to get all the chips in as opposed to lower ones.