K-series and or Duratec

[huwdm]

As some of you may have read I am looking to become a new Caterham owner having been converted from my 911.
I have been looking for an R300 or R400 Duratec but these are few and far between.
My main reason is I have driven an R300 and R500 Duratec.
Should I have any concerns if I opted for a K-Series instead (so I can get one quicker!!) or should I hold out for a Duratec.

[huwdm]

What about a 150bhp superlight Sigma engined car?
My worry is that after a few months I would want more, especially after having driven an R300 and R500.

[huwdm]

I didnt want to start a K vs Duratec row so thanks for all the comments.
As a newbie seems to be all things progress over time and the Duratec is a progression.
The K-series obviously has been there a long time and continues to have many satisfied customers.
I think I will hang on for a Duratec or Cosworth (any views on Duratec vs Cosworth?).
The next things is to find one so if anyone sees an R300 or R400 Duratec for sale please let me know - maybe I should offer a finders fee!!