Silent Hunter question

Hi all, Im new to these forums and have decided to join after making the decision to buy a good submarine sim. Thus I have chosen the Silent Hunter series of games

However my question is this, should I buy 4 or 5 based on my prediciment which is as follows;

-As much crap as i see about 5 being buggy, It seems that many people are quite happy with it after they download mods, which is acceptable for me
- I also really want 5, since it deals with the atlantic side of things which I am more interested in since I for some reason hate US subs of WWII(Something about the look of each one just irks my nerves )

-However, from what I have seen, the graphics seem very computer intensive and from what Ive seen on some peoples sigs, I assume Id need a beastly computer to run this game, which I dont have, what I do have is a computer that runs flight simulator x just fine with medium to medium high for all the graphics settings.

-Thus I come to the prediciment wether it would be better suited for me to get Silent Hunter 4 instead? seeing as how it is older and may run at higher graphics easier??

Thanks for any and all answers have a great day

Casey Smith US Navy