It will affect performance. Especially in modpacks. Minecraft will only use 1GB of RAM with 32 bit java but with 64 bit java you can use more than 1GB of RAM.
Most modpacks need 3GB or more to be smooth so you will end up with the packs crashing and sometimes not even loading. If it does run you end up with terrible fps.
Use the normal fov, use the recommended chunks which is 10 and if all fails backup your world saves and servers. Delete the Minecraft folder and then download it again. A clean install is always recommended when a new version of Minecraft is out.
