Improve Kanban performance? 10,000 Issues on one Project/Board split into more Boards

[Luke]

Question to the lovely hive-mind...

Assume for argument's sake I have, say, 10,000 live Issues on one single very old Project, and only, say, 5 Kanban Boards (2,000 Issues per Board!) – and so obviously I am noticing massive slowdown and performance issues... ok, so...

Assume I now split the Project into say, 20 Boards (one per "mini project", filtered by Epic/Components etc), so it's max 500 per Kanban Board – not ideal, but live-with-able...

My question is: does this actually improve performance for each Board? Is the slowness/bottleneck caused by the number of Issues in the Project (filter) as a whole, or only on each Board (filter)? 

Will I see net performance gain by breaking up one Project into many Boards like this? 

Thanks!