E on a 27 scale, is like tuning to F on a 25.5.
The distance between the first fret and the bridge of a 27 inch scale is roughly 25.5, I've measured, so it'd definitely be tighter.
btw I do notice that if you use thicker strings, the bigger surface area gives an impression of lower pressure, as the strings will be less "cutting". Thus giving the illusion of little change in tension.
whitestrat, what gauge do you use on the seventh string?