You have a plenty of options (I've tried all).
Split-screen is useful for dark conditions and fast shooting, when no other option is applicable. You'll waste a lot of shots, it takes time to get familiar to it. It's fun. It's very easy to install/uninstall it yourself.
Zoomed live view and tethered shooting are best suitable for macro and studio stills.
Focus peaking in live view is very effective, but it doesn't work with 100% zoom.
The fastest option is a chipped adapter. It enables built-in phase detection focusing (red dots it the optical viewfinder). I've tried a lot of adapters. The cheapest ones worked best for me. I tuned 5DII inner focus adjustment for each lens (and wrote down the settings). Works perfect (except macro range). Programmable chips (with focus correction) were so wrong at default "0", almost useless. 600D lacks inner focus adjustment.
In any case, you need widely opened aperture.