I will go against the grain. Here is my opinion:
1) Practicing on a bigger table will NOT make you a better player. It will make zero difference
2) Practicing on smaller pockets will NOT make you a better player. It will make zero difference.
3) Practicing on tougher equipment IS harder, for sure. But making something harder does not translate to making you better at it. You will simply miss a bunch more balls. You are not magically going to improve your stroke, hand eye coordination, thinking, nerves, desire, etc, on tougher equipment.
4) The patterns on 6 foot bar boxes and 10' tables, and everything in between, are the same. The easier equipment allows you to get away with some poorly hit shots, and poorly planned position routes. But you can, and should, plan for proper routes on all size tables.
5) The main difference on a 10' table is you might have to play position differently to reach shots if you are not super tall.
6) The speed control between different sizes takes about 2 shots to get perfect.
7) Before you even consider a Diamond, you better play on one in your locale with 2 year old cloth. Make sure you still like it before you commit to a new one. Their rail reaction is unlike any other table, ESPECIALLY when the cloth is worn.