I'd deffo agree with the gatorskins, for the mileage you do I'd say the cost of buying them outweighs any insignificant benefit from the 4 seasons.
I use rigid 25s for my everyday bike loaded and unloaded and they'll do 45mph perfectly fine and corner decently too. You could probably go for folders in 23s (220g same as the 4seasons) if you wanted but the 25s go up to 120psi anyway.
They have the slightly older version for £20 at wiggle http://www.wiggle.co.uk/continental-ult ... road-tyre/
these are the Ultra gatorskin (newer ones are referred to as just gatorskin) I've got both and there's no difference apart from the lettering on the side.
1958 Carlton Super Python
1990's Gitane VITUS GTI Triple Butted
1996 Raleigh Titanium Special Products Division
2007 Specialized Globe Pro
2007 Specialized Globe Expert Ultegra 6700
KTM Strada 6000 Carbon Dura Ace 9000