8/9/10 speed chainring and cassette help

Hi there all,

Newbie to the forum, although have been peeking through the curtains for a while...

I've got a bit of a conundrum that you might be able to help with; in fact it might be a non-issue.

Currently riding a Trek 1.1 kitted out with Shimano Sora stuff. Changing the 8 speed cassette to an 8 speed Sram cassette with 8 speed chain (Sram).

I didn't really want to bother changing to anything other than 8 speed as I'd then have to change the shifters. Right? (although I did get a bit carried away looking at Ultegra bits...)

It's got some standard Bontrager 5 arm crank arms and a 53/39T double chainring.

I also want to change the chainrings but am struggling to find any 8 speed in the same size (which I'm largely happy with). I can find the right T size in, what the manufacturers call 10 speed. So the question really is whether I can use a 53/39T 10 speed double chain ring (and change the chain to a narrower one?) or I have to persevere with finding an 8 speed set-up?

Sram also provide a (3mm/4mm) measurement which I assume would indicate whether I have to use a narrower chain or not? Right?

Thanks for any help.
Boz