You might wish to look at the Build Your 2005 Boxster configurator at www.niello.com. Please excuse our low Porsche prices in the USA.

Although its US market info, I doubt if the leather packages
have different bits for different markets.

As for interior color to match Seal Grey, I suggest black. Its easiest to keep clean, looks classy and purposeful. As for the other interior colors, personally I think that the color matched steering wheels they come with look a bit over the top and are tricky to keep looking nice.

The new 2005 Boxster 6spd has the same gear ratios for both Boxtser models. I cant imagine how ratios designed for a 276 hp motor will work optimally for a 240 hp motor. By all means get the 5 spd. At resale you won't lose anything
more for not having a 6spd, in fact it might be more attractive to certain buyers.

I would really like to see some data for 0-100mph times
for a std Boxster comparing the 5spd and 6spd manuals. As third gear has a longer ratio in the 6spd, the 5spd might be quicker.