Hey Sailor,
Have you ever tried poling or will your pole be the first you use? I ask because I think that diameter, finish, etc is kind of a preference thing.
I own and learned on a 50 mm. My home pole is a 50 mm Xpole Sport in chrome. The studio I workout at has both 50's and 45's. I tried a 45 for the first time last month. The major differences I observed were with the hand and leg grip, which is what you will hear commonly about the size difference. Hand grip is better on a 45, especially for smaller hands, however personally I found things requiring a lot of thigh grip (i.e. pole sits, CAR) to be more difficult. Also, I bruised as bad as when I started a year ago on the 45, I guess that may have been a readjustment thing though.
Also, take into consideration that 50 mm is usually the standard at competitions. If that's something that may interest you and you will only be working at home, you may want to keep that in mind when you purchase your pole. The instructor's pole at our studio is a 45 and my instructor told me recently that since she's been working on 45 mm for the last few months since it's been installed she now struggles with tricks on the 50 mm that she learned on a 50!
Finally, just a suggestion. If you have the extra money and are really dedicated to the idea of pole I'd invest in an Expert pole. When I started out I was intimidated by spin mode and thought I'd never even want to try it. Now that I've been doing it longer, I have been interested in spin and can only do it at the studio. Wish I would have just invested to have a spinning pole at home too. Keep in mind you can choose to be on static or spin with the Expert.
Also, you may want to search StudioVeena.com for more feedback on the different Xpole sizes, finishes, etc. There are LOTS of posts on this discussion.
Good luck on starting your pole journey <3