the couple of times I've given her finger sized foods she just rams it in her mouth and I'm worried she will have too much in her mouth and choke
This is completely normal. It is very unlikely that she will choke. She will gag - which is different from choking. Gagging is noisy and its how baby learns to move food around her mouth. Its normal. Choking is different - its silent and must be dealt with immediately. Mine gagged all the time and never choked.
my concern is allowing her to feed herself. If I give her some toast I tear off the portion size and give it to her which she is fine with this...
that is great - sounds like baby is doing well
I just can't sit and watch her try and ram half the portion in her mouth at once!
You need too. It is how she will learn. Its scary for parents but its completely normal. But you need to let your baby learn.
would it be better for me cut the the food up into smaller pieces i know she won't choke on and let her pick it up & eat it this way and over time make the pieces bigger?
No chip sized pieces that she can hold in her hand are the best way to go.
Or stay as I'm with spoon feeding her?
You could but for how long? She needs to learn.
The main reason I wanted to try more finger foods was for when we go out & about and have picnics etc
Definitely the best way to go. Plus it is just much more fun.