Add PyExcelerate as Excel Writer Engine
Here's an example with just 65,000 elements (it's _much_ worse with 250,000) so I can compare xls and xlsx:

from pandas import *

df = DataFrame({'col1' : [0.0] \* 65000,
                'col2' : 1,
                'col3' : 2})

%timeit df.to_csv('sample.csv')
10 loops, best of 3: 109 ms per loop

%timeit df.to_excel('sample.xls')
1 loops, best of 3: 8.35 s per loop

%timeit df.to_excel('sample.xlsx')
1 loops, best of 3: 1min 31s per loop
