GPU mining is pretty much Dead. Its all Asics now.
An given comparison.
You can go and spend $45-$55 per Usb Block Eruptor in the Bitcoin market.
And it will yield you about 333 Mhash/Sec. They consume 2 watts each
and the size of your thumb.
Now you can go spend $300 pick up a HD 7970 at rates of 600 Mhash.
Alt mining is generally ~300% profitability, sometimes more.
http://www.coinchoose.com/600 *3X(Profitability of scrypt) = 1800 Mhash equivalence at Bitcoin mining.
So its like 1.8 Ghash in equivalence basically for $300.
333*6= 1998 Mhash.
2Watts 6=12 Watts.
So you get more Hash rate, About 15 times less power, silent.
Size of your thumb, and its just more convenient.
GPU is DEAD. You need to move away from it.
And switch to Usb block eruptor if you want to continue mining.
And even so there are even more efficient mining ways out there.
You're missing something important. Is the 300% profitability constant? or will it increase over time. For example lately LTC is hovering around 900 difficulty lately, not changing very much. it's possible that you can still mine about the same ballpark amount of LTC in 6 months as you do now, however the BTC difficulty is going up like crazy, you will definitely get much much less BTC for GH in future. Food for thought.
In summary: Dear everybody doing mining maths, the mining numbers right now can not be use to calculate future profits without taking into account changes in difficulty.