When to split a database table instead of adding more columns - Performance - Database Design

Okay the question is add more columns or split database table.

Assume that i have a table which keeps

UserId -PrimaryKey
Col1
Col2
Col3

Now i will keep another data as Col4 Col5 But these data won't be valid for every UserId

Lets say there are 2 million records at my main table and These additional datas will be valid for only 25000 records. So the question is should i compose another table as

UserId -PrimaryKey
Col4
Col5

or

use my main table as

UserId -PrimaryKey
Col1
Col2
Col3
Col4
Col5

Which way i should do ? i care about performance. These additional cols are tinyBit and will be default 0 not null

SQL server 2008 R2