In pursuit of smooth experience with my Nexus 7 .. (currently on CynogenMod)

I've been meaning to find a smooth Android experience with a 2012 "grouper" Nexus 7, which is apparently too much to ask.

I got this device second handed and it was on 5.0 Lolipop and was laggy. I flashed CM 11 and was still laggy. Upgraded via OTA to latest build, which I believe was M12 snapshop, and got worse.

After a week o Googling around, I wiped all partitions (except my internal SD Card), mounted them and "fstrim"-ed partitions to fix any fragmented empty space, even though it was fixed in 4.2. I tried LagFix with no luck. Also removed apps to free up space, no luck. Disabled Google Currents (which is obsolete now), disabled location services, whatever I could find on the net, done with no result.

Finally I flashed "cm-11-20141112-SNAPSHOT-M12-grouper" and "gapps-kk-20140606-signed" and restored my backups with Titanium Backup and still have lag.

I have several questions but I keep it simple for now:

1) Since I backed up my apps from the laggy roms, are they defective? At least their "user data"?

2) I just want a smooth android experience so I can safely test my games on it. Am I on a wrong foot with CM? Is there "better" ROMs for my need? (I know it's unholy to talk about pros and cons of roms, at least in other forums is, but I'm on the verge of my sanity)

Thanks.