I bought a new 25mm Michelin pro3 tyre off eBay a bit back. I thought I'd bought a 23, but that's my fault for not noticing!
Honestly how much of a difference is 2mm gonna make? I have mounted it on the back and at 120psi it feels fine! Sure it'll be marginally heavier, but if I put the same on the front is it likely to have a huge effect?