The G Pad GPE is surely faster than the "LG one" (V500) but you would have to give up, among other things, Knock On, the IR Remote and full SDcard support and those are huge deal breakers for me.
LG's ROM is most certainly slower and laggier than stock Android but it's also way more feature complete (which is probably also *why* is slower...). Features that I do use, and besides the ones just mentioned, there are dozens of things like Quickmemo, the overlay apps (QSlide), the keyboard with the numbers row, the volume and brightness sliders and on and on...
All of these talks about "bloatware" (both for Samsung and for LG ROMs) really piss me off... this "bloatware" are SOFTWARE FEATURES which other ROMs generally LACK and which for the most part I do find useful (one above all, Samsung MultiWindow)!! (and most if not all of which you can uninstall/freeze/disable if you don't use it anyway!!)
It reminds me of iOS users who used to rave (they can't anymore since from iOS7 theirs has become a slower and laggier operating system, not to add far, far buggier!!) about the smoothness and fastness of their toy operating system while it was doing sweet F-all compared to Android (no real multitasking, no widgets, no powerful notification center, no live wallpapers and so on) !!
On older Samsung smartphones and tablets I have found that it's only the launcher to be sometimes "slow", not the overall ROM. For example, I use Nova Prime on my Note II (stock, rooted ROM) and I am very satisfied with its performance and with the SW features which are better done and more "coherent" than anything else out there for the Note II. Once you "complete" it with Xposed and the AppSettings and NFClockscreenoffEnabler modules it's the ultimate smartphone for the poweruser... (well, the second best after the Note 3 actually
Anyway, I don't do stupid themes, live wallpapers, CPU intensive useless "esthetic" stuff, I don't even play games on my mobile devices but I am a poweruser who takes full advantage of the PC-like capabilities of Android devices (as a quick hint, I have 64GB cards in both my Note II and G Pad and they are full of the same most used files I use on my Windows 7 PC) and the G Pad, once setup with the apps and services I use IS S-L-O-W. Getting back to the home is slow and the tablet "freezes" for a couple of seconds before accepting any input, widgets take a while to load, rotation is slow etc
...or, is it?!?
Yesterday I finally had some time to spare (I have had my G Pad since less than a month and that has been a very busy month) and finally got around installing and properly setting up Nova Prime which I had been very happily using on my OG Note and got on my Note II since day 1 and the results on the G Pad are IMPRESSIVE! It solved most of my complaints about it being slow, it really feels like having a new tablet and it's now finally a pleasure to use! Everything I listed above is FASTER and even battery life seems to have improved (I need at least another couple of days to be sure it's not a placebo effect LOL).
In other words... DO IT! DO IT NOW!
You will get a much better, powerful and feature complete launcher to boot! I even like it a lot better looks-wise.