13 million record table, growing to 25 million+

[kevin]

I've currently got a mysql (version 4.0.20-standard) MyISAM table that has about 13 million records in it. According to show table status:
Data_length = 1383705612
Max_data_length = 4294967295
Index_length = 169360384

Writes to that table are quite predictable on an annual basis, so I'm fairly certain that will grow to about 25 million records or so within the next 9 months.

So far, performance has been exceptional.

What, if any, long-term performance benefit would I get by breaking out that into multiple tables? Meaning, would I be avoiding potential performance issues in the future by breaking out this one large table into mutiple smaller tables, one per year's worth of data? It would be quite easy for me to do from an application perspective.

Thanks!