All other things being equal moving weight to the edge improves speed stability. Moving weight to the edge while reducing mass, so that the overall mass goes does but the rotational inertia of the platter stays the same reduces bearing noise. Or you could mod it in between the two, lighter but with more rotational inertia.
To work it out you'd have to do the math and that requires having a geometric model of the part and knowing the density.
I had a 25mm acrylic platter for my P5 from a German guy, The Acrylteller. Beautiful platter, same weight as the Rega glass one but with mass concentrated in the last 70mm towards the outside edge.
To be fair any acrylic platter is unlikely to give more than a couple of % increase in rotational inertia unless it's a good % heavier than the outgoing rega platter.
If you want speed stability get a TT-PSU, you'll already have reaped a fair chunk of speed improvement with a new inner. When I measured my Rega one it was 0.3mm high at two spots, so added a 1.1hz wow to everything (2 spots per rev = 66.6 per minute = 1.1per second deviation = 1.1hz wow). Doesn't sound like much but on low synth notes, say 25hz they warbled from 23.9 - 26.1hz which is noticeable as a harmonic. A solid metal subplatter is a great upgrade.
It doesn't look it from the pics, which are poor but the quality of his finish is miles above the UK stuff. I looked at them all. He makes the platters for Clearaudio, nuff said.
http://www.acrylteller.com/epages/es...P1%20-%20P2%22