7 inches is a great size for gaming, if that's what you want to do, primarily. The new Nexus 7 is a great choice for that.
On some games, the buttons are a bit too spread out on a 10" tablet. NOVA 3 for example was difficult to play because there were some buttons in the bottom corner, and some in the upper corner, and you had to move your hand to reach them.
I ultimately sold my Nexus 7 (2012) because I do a fair bit of reading and watching videos on my tablet, which I prefer a 10" for. I still play plenty of games on it, but not really anything as complicated as a first person shooter.
In terms of speed, they are both screaming fast, so nothing to worry about there.
Archos 101 - HTC Desire - LG G2X - Asus Transformer - Samsung Galaxy Nexus - Samsung Galaxy S III - Asus Transformer Prime - Nexus 7
Galaxy Note 2 - Sony Xperia Tablet Z