First road tyres on my gravel bike?

Last year I got a specialized diverge and started cycling again. I've loved it so far. I went with the diverge because I wanted something I could use anywhere, mostly on the roads but free enough to tackle a gravel or dirt path whenever I wanted.

After a year I've found I really enjoy the road riding and trying to rack up the distance on them. So I'm now rather than looking at bikes again, hoping to change up the diverge to be more specced to the road. I figured the tyres would be a good place to start.

The current tyres are specialized pathfinder 38mm, they have that centre slicked part and more knobbly outside edges. I saw that specialized roubaix pro 2bliss 30mm were quite cheap. £29 here in the UK. Would they be a good tyre to switch to?

I don't know too much about tyres but I've read that wider tyres have less rolling resistance, so 30mm seemed like a good compromise rather than going super skinny. The other tyres I was looking at were the Michelin Power Cup Competion Line TLR Tyre at 28mm, more slick, skinnier and come in tanwalls. Would they really make much of a difference?

Any suggestions or advice would be appreciated!