I am after opinions please.

I don't want to heavily modify my car. 1.6 3 door sport 55 plate
Sick of the huuuuge gap between arch & tyre. Is it better to buy 17s or better to lower 30/40m & stick to my 16s??

Thoughts??

personally, I would stick 17's on, but still lower it, but not slam it. would look awesome mate

You can either bung on 18's which will look good and also fill the arch a bit more or go for an eibach lowering kit which will drop the suspension by 3-4cm.

18's would work yeah, and look really good actually

but won't that knock his speedometer out of sync?

Not noticeably.
The Speedos always read over anyway so most likely 18's would make the Speedo dead on.
Best way would be to run them with a satnav on and check speed that way.
On 16's mine always shows 3mph under the Speedo reading.

ahh right, ah well, go up to 18s mate lol

probably wont b able to lower it much tho, but with wheels that big, wont need to.