Maybe the question is answered a long time ago but from what i understand there are several variables which interact with each other. I don't know any formula it's just qualitative guess from what i'd read and learned here on Steemit:

1. the more STEEM POWER you have the more weight has your vote, the bigger the better
2. the more VOTING POWER you currently have 0-100% (dependent how often you vote and how long you regenerated the VP) the more payouts you produce, the bigger the better
3. the better your timing of your vote is the more payouts go to you, before 15min you get 0.06%, after 15min you get 50% and after 30min you receive 100% curation reward. In the following post there is a more detailed timing description for voting

Is that true or has that changed already?

1.,2. and 3. are combined in some formula with a few more parameters i think. STEEM POWER and VESTS are connected. That's my simple understanding without knowing details in depth.

If you drain your VOTING POWER to maybe 13% then you've a lot less influence and a lot less payout from your vote. I tried that, it's true! :)

The 20-30 recommended upvote limit is based on the regeneration curve i think, it's not linear. If you do heavily voting, maybe 100 upvotes in a hour you'll will be at a very low VP value e. g. 15 and the refill rate (water drops per minute) is much slower in comparison to a VP value of 50 but will increase over time and may accelerate (no evidence). I think it's similar to the following chart (just a guess by me, could be a more complex function or maybe it's linear and there is a defined number of votes per day e. g. 23.2 as parameter for 100% regenerating per day, i don't know)

chart deleted by onetin84, i think VPregeneration is more linear than i thought

The prinicple for me is to not exaggerate on voteups because the VP regenerates very slowly and you must wait for days do get your full voting power back.

A fork last month changed the draining in voting power by factor 4 with a full vote (100% slider) like @sykochica explained. @andrejcibik experienced a strange slow regeneration, don't know if it's true but something to do further research on that topic if maybe no voting leads to slower regeneration and maybe you must vote wether or not you have a low VP level. Many questions .. i'm curious