it's not usually recommended to scan discs on a different drive from which they were burned, but with an LG you have little choice! for your own internal comparisons that's absolutely fine to do since you'll have a baseline to compare it to, but be wary of comparing your scans of LG-burned discs to others' scans since they may or may not be comparable. it looks like you're doing just fine though.
for the benefit of those viewing your scans be sure to post what drive/firmware the disc was burned with whenever it was not burned with the same drive doing the scanning
also, check the surface of the disc. is there any dust or dirt about halfway in where that large PIF spike is? without that PIF spike the disc would be a 98 quality score which is VERY acceptable indeed!
and as arachne stated, lowering the burn speed to 12x might reduce those jitter readings which are a bit disturbing. I'm not sure about your particular LG drive and 16x media, but I know for a fact that the BenQ 1640 doesn't fare quite as well when burning at 16x as it does at 12x.