As MaxBiceps says, Deca should be at least 200-300 mgr/week
But since you ask: yes you can gain something on this. You should be able to gain 6-8 pounds, especially since you never used anything before. You should go for 9-12 weeks. It takes a couple of weeks for both roids to give result and then you stop (as you say 6-8 weeks). Since you do not take a lot, there will not be progress in your case once you stop.
You see, Deca is long acting, but with 50 mgr you cannot profit gains for another 2-3 weeks on that dose after the cycle.
But guys taking 600 mgr/week (i don't say you should, watch out with Deca), they can still grown after the last shot, because there is a huge amount still in there body.