How much RAM can I allocate to MC?

I wanted to install a Minecraft shader: Sildur or SEUS, for 1.8, I already have Optifine, whereby my laptop has 8 GB Ram. Sildur High worked briefly, but soon got stuck (so I could only close Mc). The same with Medium & Lite. Only 'enhanced' now works properly. Now you can assign more ram via the launcher, how much can I enter there (at 8 nothing else works properly)?

By the way, I have graphics on 'Fast', fps now at 100 fps max., Visibility on 12 chunks (default), maybe there's still something to improve? Because I would have thought that a new computer with 8 Gb RAM could at least create Lite / Medium.

Guide value: Half of your RAM, if you have 16GB then 8 etc.

At 8GB I would allocate 4, maximum 5 GB and would best close Chrome or something
Set visibility to 8 chunks is enough

Half of your RAM is 4 GB

Normally there's a good computer with 16Gb RAM. You have more of an office.