There are many differences but you asked for big differences and pointed out a few of them already.Other big differences would be, it costs more $$$ in porting to bring the T-REX top end to match the power of the Cheetahs.The T-REX top end uses a billet "coolhead" type of head wich domes are interchangeable, while the Cheetah cylinders come with a cast "stock" type of head wich you will need to get machined or even changed if you want to change compression.The T-REX uses 4 transfer ports vs 6 for the Cheetahs and finally but most importantly, pretty much every shop can get the Cheetah cylinders to run well while very few can do a great job on a set of T-REX cylinders.