hey man
I used to think the same thing but beyone 2 weeks there is no real difference. 4 weeks shuts you down just as much as 12 weeks.
I believe after 12 weeks there could be some problems, but some people on here run 4-5 months and have no problems.
If you are bent on doing a short cycle use fast acting drugs. Test prop is good for a short cycle, but if you are going 4 weeks just go head and do 12 IMO. Same result on HTPA with more gains to show for it.