What do you mean doing more? Like what?
I mean by hardcore video editing.
More rendering to do means more CPU and GPU power needed.
If you plan to make a little home video, stick with the 13in. Maybe a Air might work.
But if you are doing it for professional use, making profit, for work, your own high quality satisfaction, go with 15in and up.
13in's are as the price says, a average consumer use.
Nothing high quality, you-get-what-you-pay-for.
Now the 15in, comes with dedicated GPU up to 1GB and quad core Mobile CPU.
iMac 21.5 and 27in are getting real.
27in can have up to 2GB vRAM and a DESKTOP quad core CPU.
Mac Pro, this is more of you get more than what you pay.
High quality server level internals with many GPUs and CPU upgrades.
The stock Xeon processor can pretty much do heavy video edit with other heavy work.
Maybe play some games as you edit the video.
But with 13in, if you start to edit low-mid video, dont expect it to be snappy.