There is no math needed here, but you can use Sheldon Browns gear calculator if youd like (google it). It will tell you what rpms you will need for a given speed in each gear.

If you want a bigger gear, you'll have to go to the 53-39 and keep the 11-25 cassette. The 53-11 gear will give you another mph or 2 before you spin out. The 39-25 will be pretty close to your 34-23 and since you don't use the 34-25, you wont miss that lower gear. In addition to adding to your highest gear, you may get a little less cross chaining and better shifting with the standard set up.