Pathfinder pro 38s or 42s?

Hi!

I need to change the WTB Riddlers that came with my Topstone 4 since the threading on the rear tire is very worn. Since I do a fair bit of riding on paved surfaces with some gravel and light trails in-between I was looking at the Pathfinder pro wheel. My current Riddlers are 37s I think and i was wondering how much difference the Pathfinder 42s would make. Will I be a lot faster on paved surfaces with the 38s with the 42s being much more comfortable on gravel and trails?

I've never had bigger tires than the Riddlers so I'm kind of at a loss as to what to pick here. Would appreciate your input.