Blind Structure For Home Tourney

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I want to host a two-table, 16 player home tourney that will end approximately after three and one-half hours.

In my group, we usually play eight players at T2500 and 15 minute blinds of 25/50, 50/100, 75/150, 100/200, 150/300, 200/400, 300/600, 400/800, etc . . .

We can usually get in two such tourneys w/in a four hour period.

My question is this: if I use the same blind structure, what is the deepest stack that we could start w/and still end between 3-4 hours. I'd like to start w/20 minute blinds and increase to 15 in second half if needed if the tourney is going too slow.

Not sure how to structure a two-table tourney based on how fast we play two single-table tourneys. I assume I can't just double the stacks and assume we'll finish in the desired time frame. But how much above $2500 can I go?

All comments would be welcome. Thanks.