There is a chance that you may be able to make better gains by adding more food. Over this time, you have of course gotten bigger and you will require more nutrients to maintain or grow. That being said, after a couple of years of running cyp cycles, it sounds like you are ready to do one of two things. Up the dose, or add another compound. I like your idea best. Adding a second compound will create synergy, the effect of 1+1=3 or 4. Upping the test alone would do more, but not as much as adding in deca.

The way you have cycled is ideal. You've given yourself a lot of room to make changes to your cycling and get better results. Over time, the same ol', same ol' will not have the same punch. This is why I try to caution new users away from running several compounds, right out the gate. Each steriod is a tool to continue gaining muscle. If you throw all your tools at the project right away, you aren't going to have as many options down the road. Using the least amount of gear, to evoke a great response should always be the goal. As the doses go up, the chance of side effects go up as well, and you are at great risk for compromises with your health. 

Anyway, back to your cycle. Deca would be a good compound to use. It does have potential side effects with sexual function that turn some guys off. Not everyone has this issue though and if you run more test than deca, you'll have a better chance of being ok. Deca, a 19-nor based steroid, can also be hard to recover from. It wouldn't hurt to add HCG during the cycle to help you recover your natural test after. If this is something you would rather avoid, EQ is another good option. The fluid retention isn't usually as high and the gains can have a little more "quality". If you want all out mass, deca is good. If you want to stay a little tighter, EQ is good. Deca might be a little better for strength and it can help with achey joints, where as EQ will increase stamina and endurance in the gym. I would use deca at 400mg EW or EQ at 4-500mg. If you opt for EQ, you will want to extend your cycle to 16 wks. I will give you an example of both cycles. Also, I would also opt for a test ester other than cyp. 

1-14

Test E 500mg

HCG 250iu 2x wk

adex .5mg 2x wk to EOD, as needed

1-12

Deca 400mg EW

PCT would start 2 wks after your last injection. 

EQ cycle :

1-16

Sust 500mg EW

EQ 500mg EW

adex .5mg 2x wk to EOD, as needed

PCT starts 3 wks after last inection