Response Time Differences

if those numbers are not exaggerations or other weasely way to minimize the facts, NO.
You won't see 8ms and below ghosting, or 12ms, for that matter... even at true 16ms.
With true measurements, anything below 16ms is great.

If u play games usually like u say %80, u should get a 4 ms or <4ms lcd..
For example Vx922 has 2ms response time (2 ms g-t-g, 2 ms b-w-b)
I suggest u to take a look at that lcd. If u play games like that percents, then I don't suggest u 12 or 16ms response time.. Btw what ll u use the %20 for ?

I use a Dell 2405FPW with a X1800XT and game about 5 to 10 percent of the time... I gotta work and post here too.
My monitor is rated 12ms but Toms clocked it at closer to 20ms.
Either way, it plays Doom 4, FEAR and others fukinfantabulously to my eyes!!

Are you anally obsessed with minor faint obscurities that 90% of the population can not detect?
If so, get the 4ms one.
If ultimate perfection is not at the very core of you existence, then save some cache.

Read some reviews from Google, enter "make/model" and the word "review"
You will get plenty of sites professionally reviewing your model, and then make a decision.