now then boys and girls why indeed.
after a little search, it seeems most convert to 520 and around 14/45. as far as i can make out this is for choose and availabilty of sprockets but are there any other reasonable issues other then 'because we can'.
stock 3tj as we all know is 428 and 19/55, which is near enough the same as 520 14/45.
i'm wanting to stay stock ratios with a 4he in (cause i only have to buy a front sprocket), anyone experenced any problems or foresee any issues

thank all

Because a 520 is a more standard size and more important the torque on a 600 is higher. You can run a thou on a 520 so it isn't going to wear out (percievably) as quickly as the 428, this is good for a road bike.

If you're running a race bike then go with the lighter chain because you want performance rather than chain life.

I use non o-ring 520s on all my bikes (400, 550 & 600 IL4s and a couple of 660 singles), just because it's easy to get the sizes you want and I'm impatient