Looking to fill any gaps in my current 4 ball arsenal.
Lock
Eternal Cell
Hyper Cell Skid
Byte
Hy Road 

You've got 5 balls listed...

You certainly don't have any weak balls, but if you're super speed dominant, you may never need one. In other words, it's impossible to guess without knowing anything about how you throw and what you throw on.

I do throw the ball on the faster side.  Trying to correct that.  I got the hy road thinking it was on the weaker side but its not too weak.  Eternal cell and skid are close.  EC is about 2-3 boards stronger.  As far as the byte it seemed to have died on me.  Probably gonna replace it.

Any roto grip balls that would fill in the gaps?

If you're only bowling on a THS, your arsenal looks fine. However you only have one symmetrical ball. If you do ever bowl on flatter oil patterns, I would suggest a smooth, early rolling symmetric. Something like the IQ Tour Solid (although you may need to rough it up a little more). However, being speed dominant I would highly recommend purchasing a Haywire. It's got a low RG core wrapped around Roto Grip's most aggressive cover. It would give you a strong motion while being able to control the mid-lanes. Would definitely be a great addition to your Arsenal.

Hope this helps!

I would also suggest the IQ Tour Solid as it will give you a low RG/lower flaring ball that can complement your Hy-Road at the lower end.  If you bowl on flatter patterns, it is one of the better balls you can have.

Or, another potential option would be to drill a second Hy-Road.  On the second Hy-Road, you can always tweak the cover and/or tweak the layout by changing the pin placement along with the drill angles.  In combination with that, you could always punch a x-hole to reduce overall flare.  This way you'll get something you're familiar with but with a different reaction that you could basically ball down to.