Well there are two ways to measure speed on your boat. Speed through the water would be best measured with a knot meter. Speed over ground can be measured with a GPS. I do not have a working knot meter on my boat. The top speed over ground I ever saw on my GPS on my E-27 was 9.1 knots and that was only for a fraction of a second on a broad reach surfing down a wave in about 24 knots of wind.
You can calculate the Hull Speed of your boat, "used to provide an approximate maximum efficient speed for a hull."
I think the basic formula is 1.34 times the square root of the length of the water line.
http://en.wikipedia.org/wiki/Hull_speed
I have enjoyed messing around with this site Carl's Sail Calculator v3.53.
You can look up the specs on you boat or do comparisons with other boats.
http://www.image-ination.com/sailcalc.html
According to Carl's Sail Calculator your Hull Speed for a E-25+ is 6.3