I can only assume everyones geno type is different and can play a part in how fast or slow your body responds to your gear in a given cycle alongside your own individual input, diet, training, pct..etc. I also have just finished week 4 of my cycle of Test E as well with no sides but with a good amount of gains. I began at 162lbs I then increased my weight to 171lbs natural (I just finally started to really get serious about the base of everything and that was my diet.) Im now at 181lbs and pretty lean, so far Ive gained a good 10lbs on the gear with little water retention. Here are my stats:

Age 28yrs
Ht 5'11
Wt Before cycle 162lbs Current 181lbs.
BF% 8-10%
Training 5yrs (Last 3yrs of serious training)
Diet 3000-3500 cals per day
Experience: First cycle however 5yrs of just reading and educating myself on anabolics.
Gear 500mg Test E. split 2 shots per week at 250mg Mon/Thur
PCT Nolva

Damn! sorry guys I just freakin wrote you a novel..lol