i have a pretty warm 5k in a little ke15. it is faster than my old worked 4k, which would eat the majority of v6 commodores and AU and earlier 6 falcons. the 5k is good, but there is a need for more power. it gets 8L/100kays on average too.
a ke70 is a good 2 and a half adult passengers heavier than a ke15.
i just don't understand why you wouldn't make use of the extra engine bay room in a ke70. with mine i have space constraints and need to start cutting up shit to make a larger engine fit, you guys with ke70s don't.
3Ts have way more potential than a K series. really they are just an uprighted oversized hemi headed progression, not to mention cross flow. i have heard of 7, 8, and 9 sec full house 3Ts with forced induction. never a K engine anywhere near as quick.
4ks are good for economy, but not much else. sure you can make them nifty, but power to weight is the limiting factor. a lighter car helps, if you want to have fun with them. guess it comes down to what you consider is fast enough.