I can't comment on wether it till fit your non turbo, but I can tell you about the 6 speed. I had the 5 speed in my old 1.8t 150 and have the 6 speed in my new 1.8t 180.
I'm not so sure about the 6 speed myself. With the 5 speed I seem to remember it would do 41 in 1st, 72 in 2nd, 100 in 3rd, 120 in 4th and 140+ in 5th. Motorway cruising at 70 was about 3500 rpm I think.
But with the 6 speed they closed the ratios down, I'll have to 'test' it, but I think 1st is about 39 and 2nd is about 65 so you get less speed in gears and have to work more. Motorway cruising at 70 is about 3300 rpm I think, so I'm not sure what the advantage is, 6th is certainly not an 'overdrive' gear.
I've got a couple of mates with GTI 150 Diesels, I'm sure they said motorway cruising is much lower/quieter revs in 6th gear.
I'll check my speeds in the 6 speed again, but I'm pretty sure the speeds in the 5 speed are accurate as I've done over 170,000 in 2 different GTI 5 speeds.
Not sure if the "speed in gears' tests are the best, but there you have it, would be interested to see what other people think.