Couple of things I found out
1) 05 onwards use larger axles, so although the SVX auto stubs will go in, you'll need to swap out the oil seals to the early 6 speed seals.
2) I had the Legacy ratios which were the same 1st to 4th, with the slightly taller 5th and 6th...didn't seem to make that much difference on the road, but for road cars, I would probably recommend it
3) The 05 or later STI's changed ratios from 2nd to 6th. They were very different...much wider spaced. Check out the following as an example
http://sti.subaru.com.au/showroom/im...pecifications/
For my money, and for a road car, I'd reckon the lastest 6 speed out of the Legacy's might be a better option. Ratios even taller again, great for cruising, and nowhere near as heavy as the current STI 6 speed. Check out ther ratios (compared to the above link) here
http://www.subaru.com.au/models/libe...fications/all/
And before anybody asks, it's behind the current spec 2.5 turbo with 195kw and 300nm of torque. More than enough for an SVX.
Just my two bobs worth.
M